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Hindawi Publishing CorporationInternational Journal of Mathematics and Mathematical SciencesVolume 2013 Article ID 504645 8 pageshttpdxdoiorg1011552013504645
Research ArticleGeometric Methods to Investigate Prolongation Structures forDifferential Systems with Applications to Integrable Systems
Paul Bracken
Department of Mathematics University of Texas Edinburg TX 78541-2999 USA
Correspondence should be addressed to Paul Bracken brackenutpaedu
Received 8 January 2013 Accepted 13 February 2013
Academic Editor Aloys Krieg
Copyright copy 2013 Paul BrackenThis is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
A type of prolongation structure for several general systems is discussed They are based on a set of one forms for which theunderlying structure group of the integrability condition corresponds to the Lie algebra of SL(2 R) O(3) and SU(3) Each will beconsidered in turn and the latter two systems represent larger 3 times 3 cases This geometric approach is applied to all of the three ofthese systems to obtain prolongation structures explicitly In both 3 times 3 cases the prolongation structure is reduced to the situationof three smaller 2 times 2 problems
1 Introduction
Geometric approaches have been found useful in producinga great variety of results for nonlinear partial differentialequations [1] A specific geometric approach discussed herehas been found to produce a very elegant coherent andunified understanding of many ideas in nonlinear physicsby means of fundamental differential geometric conceptsIn fact relationships between a geometric interpretationof soliton equations prolongation structure Lax pairs andconservation laws can be clearly realized and made use ofThe interest in the approach its generality and the resultsit produces do not depend on a specific equation at theoutset The formalism in terms of differential forms [2]can encompass large classes of nonlinear partial differentialequation certainly the AKNS systems [3 4] and it allowsthe production of generic expressions for infinite numbers ofconservation laws Moreover it leads to the consequence thatmany seemingly different equations turn out to be related bya gauge transformation
Here the discussion begins by studying prolongationstructures for a 2 times 2 119878119871(2R) system discussed first by Sasaki[5 6] and Crampin [7] to present and illustrate the methodThis will also demonstrate the procedure and the kind ofprolongation results that emerge It also provides a basis fromwhich to work out larger systems since they can generally be
reduced to 2 times 2 problems Of greater complexity are a pairof 3 times 3 problems which will be considered next It is shownhow to construct an 119874(3) system based on three constituentone forms as well as an 119878119880(3) system composed of eightfundamental one formsThe former has not appearedThe 3times3 problem is less well known than the 2times2 problem howeversomework has appeared in [8 9] In the first of these the 3times3solitons degenerate to the AKNS solitons in three ways whilein the latter nondegenerate case they do not All of the resultsare presented explicitly that is the coefficients of all theforms and their higher exterior derivatives are calculated andgiven explicitly Maple is used to do this in the harder casesThe approach is quite unified and so once the formalism isestablished for the 119878119871(2R) system the overall procedure canbe carried over to the other Lie algebra cases as well
Of course the 3 times 3 problems will yield more types ofconservation laws The prolongation structures of the 3 times 3
problems will be observed to be reduceable to the same typeas the 2 times 2 system considered at the beginning Howeverthe Riccati representations become much more complicated[10]The generalization of this formalism to an 119899times119899 problemthen becomes straightforward after completing the study ofthese smaller cases [11]The prolongation structure of an 119899times119899problem is reduced to a collection of 119899 smaller (119899minus1)times(119899minus1)cases and finally at the end to a set of 2 times 2 problems such asthe 119878119871(2R) case at the beginning Finally to summarize at
2 International Journal of Mathematics and Mathematical Sciences
the end a collection of conservation laws are developed fromone of the results and some speculation as to how this typerelates to other procedures [12 13]
2 119878119871(2R) Prolongations
The procedure begins by associating a system of Pfaffianequations to the nonlinear system to be studied namely
120572119894= 0 120572
119894= 119889119910119894minus Ω119894119895119910119895 119894 119895 = 1 2 (1)
In (1) Ω is a traceless 2 times 2 matrix which consists of afamily of one forms 120596
119894 At the end it is desired to express
these one forms in terms of independent variables which arecalled 119909 and 119905 the dependent variables and their derivativesHowever no specific equation need be assumed at the startThe underlying structure group is 119878119871(2R) Explicitly thematrix of one forms is given by the 2 times 2matrix
Ω = (1205961
1205962
1205963minus1205961
) (2)
The integrability conditions are expressed as the vanishing ofa traceless 2 times 2matrix of two forms Θ given by
Θ = 119889Ω minus Ω and Ω (3)
In terms of components the left-hand side of (3) has the form
Θ = (Θ119894119895) = (
1205991
1205992
1205993minus1205991
) (4)
Substituting (2) into (3) a matrix which contains the integra-bility equations in terms of the basis one forms is obtainedThe three equations are
1205991= 1198891205961minus 1205962and 1205963 120599
2= 1198891205962minus 21205961and 1205962
1205993= 1198891205963+ 21205961and 1205963
(5)
Of use in the theorems which follow it is also useful to havethe 119889120596
119894in (5) expressed explicitly in terms of the 120599
119894as
1198891205961= 1205991+ 1205962and 1205963 119889120596
2= 1205992+ 21205961and 1205962
1198891205963= 1205993minus 21205961and 1205963
(6)
Therefore by selecting a particular choice for the set 120596119894 the
nonlinear equation of interest can be written simply as
Θ = 0 120599119894= 0 119894 = 1 2 3 (7)
It is easy to see that the system is closed Upon differentiatingΘ and substituting (3) we obtain
119889Θ = Ω and Θ minus Θ and Ω (8)
This implies that the exterior derivatives of the set of 120599119894 are
contained in the ring of two forms 120599119894
Now the differential ideal can be prolonged by includingthe forms 120572
1 1205722 given by (1)
Theorem 1 The differential one forms
1205721= 1198891199101minus 12059611199101minus 12059621199102 120572
2= 1198891199102minus 12059631199101+ 12059611199102 (9)
have the following exterior derivatives
1198891205721= 1205961and 1205721+ 1205962and 1205722minus 11991011205991minus 11991021205992
1198891205722= minus 120596
1and 1205722+ 1205963and 1205721+ 11991021205991minus 11991011205993
(10)
Hence the exterior derivatives of the 120572119894 are contained in the
ring of forms 120599119894 120572119895
Proof The forms (9) follow by substituting (2) into (1)Differentiating 120572
1in (9) it is found that
1198891205721= minus11991011198891205961+ 1205961and 1198891199101minus 11991021198891205962+ 1205962and 1198891199102 (11)
Obtaining 1198891199101and 119889119910
2from (9) and 119889120596
1 1198891205962from (6) 119889120572
1
becomes
1198891205721= minus11991011205991minus 11991011205962and 1205963+ 1205961and 1205721+ 11991021205961and 1205962minus 11991021205992
minus 211991021205961and 1205962+ 1205962and 1205722+ 11991011205962and 1205963minus 11991021205962and 1205961
= 1205961and 1205721+ 1205962and 1205722minus 11991011205991minus 11991021205992
(12)
Similarly beginning with 1205722
1198891205722= minus11991011198891205963+ 1205963and 1198891199101+ 11991021198891205961minus 1205961and 1198891199102
= minus11991011205993+ 211991011205961and 1205963+ 1205963and 1205721
+ 11991011205963and 1205961+ 11991021205963and 1205962
+ 11991021205991+ 11991021205962and 1205963minus 1205961and 1205722minus 11991011205961and 1205963
= minus1205961and 1205722+ 1205963and 1205721+ 11991021205991minus 11991011205993
(13)
as required
Corollary 2 The exterior derivatives of the 120572119894in (9) can be
expressed concisely in terms of the matrix elements ofΘ andΩas
119889120572119894= minusΘ119894119895119910119895+ Ω119894119895and 120572119895 119894 119895 = 1 2 (14)
The corollary is Theorem 1 after using the definitions ofthe matrices in (2) and (4)
The forms 1205721 1205722given in (9) lead to a natural Riccati
representation called 1205723 1205724for this differential system This
arises by taking the following linear combinations of 1205721and
1205722
1199102
11205723= 11991011205722minus 11991021205721
= 11991011198891199102minus 11991021198891199101minus 1199102
11205963+ 2119910111991021205961+ 1199102
21205962
1199102
21205724= 11991021205721minus 11991011205722
= 11991021198891199101minus 11991011198891199102minus 1199102
21205962minus 2119910111991021205961+ 1199102
11205963
(15)
International Journal of Mathematics and Mathematical Sciences 3
Two new functions or pseudopotentials 1199103and 119910
4can be
introduced which are defined by the transformation
1199103=1199102
1199101
1199104=1199101
1199102
(16)
Then from (15) the following forms which have a Riccatistructure result
1205723= 1198891199103minus 1205963+ 211991031205961+ 1199102
31205962
1205724= 1198891199104minus 1205962minus 211991041205961+ 1199102
41205963
(17)
These equations could also be thought of as Riccati equationsfor 1199103and 119910
4
Theorem3 (i)Theone forms12057231205724given by (17) have exterior
derivatives
1198891205723= 211991031205991+ 1199102
31205992minus 1205993+ 21205723and (1205961+ 11991031205962)
1198891205724= minus 2119910
41205991minus 1205992+ 1199102
41205993+ 21205724and (minus120596
1+ 11991041205963)
(18)
Consequently results (18) are contained in the ring spanned by120599119894 and 120572
119895
(ii) Define the forms 1205901= 1205961+ 11991031205962and 120590
2= minus120596
1+
11991041205963appearing in (18) The exterior derivatives of 120590
1and 120590
2
are found to be
1198891205901= 1205991+ 11991031205992+ 1205723and 1205962
1198891205902= minus1205991+ 11991031205992+ 1205724and 1205962
(19)
Therefore 1198891205901equiv 0 and 119889120590
2equiv 0 mod 120599
119894 120572119895
The proof of this Theorem proceeds along exactly thesame lines as Theorem 1 The 119878119871(2R) structure and theconnection interpretation can be based on the forms 120572
3 1205724
At this point the process can be continued Two morepseudopotentials 119910
5and 119910
6can be introduced and the
differential system can be extended by including two moreone forms 120572
5and 120572
6 The specific structure of these forms is
suggested byTheorem 3
Theorem 4 Define two one forms 1205725and 120572
6as
1205725= 1198891199105minus 1205961minus 11991031205962 120572
6= 1198891199106+ 1205961minus 11991041205963 (20)
The exterior derivatives of the one forms (20) are given by theexpressions
1198891205725= minus1205991minus 11991031205993minus 1205723and 1205962 119889120572
6= 1205991minus 11991041205993minus 1205724and 1205963
(21)
Results (21) specify the closure properties of the forms 1205725and
1205726 This theorem is proved along similar lines keeping in mind
that the results for 1198891199103and 119889119910
4are obtained from (17)
A final extension can be made by adding two additionalpseudopotentials119910
7and1199108 At each stage the ideal of forms is
being enlarged and is found to be closed over the underlyingsubideal which does not contain the two new forms
Theorem 5 Define the one forms 1205727and 120572
8by means of
1205727= 1198891199107minus 119890minus211991051205962 120572
8= 1198891199108minus 119890minus211991061205963 (22)
The exterior derivatives of the forms 1205727and 120572
8are given by
1198891205727= 2119890minus211991051205725and 1205962minus 119890minus211991051205992
1198891205728= 2119890minus211991061205726and 1205963minus 119890minus211991061205993
(23)
and are closed over the prolonged ideal
3 119874(3) Prolongations
The first 3 times 3 problem we consider is formulated in terms ofa set of one forms 120596
119894for 119894 = 1 2 3 The following system of
Pfaffian equations is to be associated to a specific nonlinearequation
120572119894= 0 120572
119894= 119889119910119894minus Ω119894119895119910119895 119894 119895 = 1 2 3 (24)
In (24) Ω is a traceless 3 times 3 matrix of one forms Thenonlinear equation to emerge is expressed as the vanishingof a traceless 3 times 3matrix of two forms Θ
Θ = 0 Θ = 119889Ω minus Ω and Ω (25)These can be considered as integrability conditions for (24)The closure property the gauge transformation and the gaugetheoretic interpretation can also hold for 3 times 3 systemsExplicitly the matrixΩ is given by
Ω = (
0 minus1205961
1205962
1205961
0 minus1205963
minus1205962
1205963
0
) (26)
Using (26) in (24) and (25) the following prolonged differen-tial system is obtained
1198891199101= 1205721minus 11991021205961+ 11991031205962 119889120596
1= 1205991minus 1205962and 1205963
1198891199102= 1205722+ 11991011205961minus 11991031205963 119889120596
2= 1205992minus 1205963and 1205961
1198891199103= 1205723minus 11991011205962+ 11991021205963 119889120596
3= 1205993minus 1205961and 1205962
(27)
By straightforward exterior differentiation of each 120572119894and
using (27) the followingTheorem results
Theorem 6 The 120572119894given in (27) have exterior derivatives
which are contained in the ring spanned by 1205991198943
1and 120572
1198953
1and
given explicitly as1198891205721= 11991021205991minus 11991031205992minus 1205961and 1205722+ 1205962and 1205723
1198891205722= minus 119910
11205991+ 11991031205993+ 1205961and 1205721minus 1205963and 1205723
1198891205723= 11991011205992minus 11991021205993minus 1205962and 1205721+ 1205963and 1205722
(28)
The one forms 1205721198943
1admit a series of Riccati representa-
tions which can be realized by defining six new one forms
1199102
11205724= 11991011205722minus 11991021205721 119910
2
11205725= 11991011205723minus 11991031205721
1199102
21205726= 11991021205721minus 11991011205722
1199102
21205727= 11991021205723minus 11991031205722 119910
2
31205728= 11991031205721minus 11991011205723
1199102
31205729= 11991031205722minus 11991021205723
(29)
4 International Journal of Mathematics and Mathematical Sciences
In effect the larger 3times3 system is breaking up into several 2times2systems To write the new one forms explicitly introduce thenew functions 119910
1198959
4which are defined in terms of the original
1199101198943
1as follows
1199104=1199102
1199101
1199105=1199103
1199101
1199106=1199101
1199102
1199107=1199103
1199101
1199108=1199101
1199103
1199109=1199102
1199103
(30)
In terms of the functions defined in (30) the 1205721198959
4are given
as
1205724= 1198891199104minus (1 + 119910
2
4) 1205961+ 119910411991051205962+ 11991051205963
1205725= 1198891199105minus 119910411991051205961+ (1 + 119910
2
5) 1205962minus 11991041205963
1205726= 1198891199106+ (1 + 119910
2
6) 1205961minus 11991071205962minus 119910611991071205963
1205727= 1198891199107+ 119910611991071205961+ 11991061205962minus (1 + 119910
2
7) 1205963
1205728= 1198891199108+ 11991091205961minus (1 + 119910
2
8) 1205962+ 119910811991091205963
1205729= 1198891199109minus 11991081205961minus 119910811991091205962+ (1 + 119910
2
9) 1205963
(31)
To state the next theorem we need to define the followingthree matrices
Ω1= (
211991041205961minus 11991051205962
minus11991041205962minus 1205963
11991051205961+ 1205963
11991041205961minus 211991051205962
)
Ω2= (
minus211991061205961+ 11991071205963
1205962+ 11991061205963
minus11991071205961minus 1205966
minus11991061205961+ 211991071205963
)
Ω3= (
211991081205962minus 11991091205963
minus1205961minus 11991091205963
1205961+ 11991091205962
11991081205962minus 211991091205963
)
(32)
Theorem 7 The closure properties for the forms 1205721198949
4given in
(31) can be summarized in the form
119889(1205724
1205725
) = (minus (1 + 119910
2
4) 1205991+ 119910411991051205992+ 11991051205993
minus119910411991051205991+ (1 + 119910
2
5) 1205992minus 11991041205993
)
+ Ω1and (
1205724
1205725
)
119889 (1205726
1205727
) = ((1 + 119910
2
6) 1205991minus 11991071205992minus 119910611991071205993
119910611991071205991+ 11991061205992minus (1 + 119910
2
7) 1205993
)
+ Ω2and (
1205726
1205727
)
119889 (1205728
1205729
) = (11991011205991minus (1 + 119910
2
8) 1205992+ 119910811991091205993
minus11991081205991minus 119910811991091205992+ (1 + 119910
2
9) 1205993
)
+ Ω3and (
1205728
1205729
)
(33)
The exterior derivatives are therefore contained in the ringspanned by 120599
1198943
1and the 120572
1198959
4
In terms of Ω119894 a corresponding matrix of two forms Θ
119894
can be defined in terms of the corresponding Ω119894defined in
(32)
Θ119894= 119889Ω119894minus Ω119894and Ω119894 119894 = 1 2 3 (34)
Theorem 8 The 2 times 2matrix of two forms Θ119894defined by (34)
is contained in the ring of forms spanned by 1205991198943
1coupled with
either 1205724 1205725 1205726 1205727 or 120572
8 1205729when 119894 = 1 2 3 respectively
Proof DifferentiatingΩ1and simplifying we have
Θ1= 119889Ω1minus Ω1and Ω1
= (211991041205991minus 11991051205992+ 21205724and 1205961minus 1205725and 1205962
minus11991041205992minus 1205993minus 1205724and 1205962
11991051205991+ 1205993+ 1205725and 1205961
11991041205991minus 211991051205992+ 1205724and 1205961minus 21205725and 1205962
)
(35)
Similarmatrix expressions can be found for the cases inwhichΩ1is replaced by Ω
2orΩ3 respectively
Unlike Ω given in (26) the Ω119894in (32) are not traceless
Define their traces to be
120581119894= trΩ
119894 119894 = 1 2 3 (36)
These traces provide convenient ways of generating conser-vation laws on account of the followingTheorem
Theorem 9 The exterior derivatives of traces (36) are given by
1
31198891205811= 11991041205991minus 11991051205992minus 1205961and 1205724+ 1205962and 1205725
1
31198891205812= minus 119910
61205991+ 11991071205993+ 1205961and 1205726minus 1205963and 1205727
1
31198891205813= 11991081205992minus 11991091205993minus 1205962and 1205728+ 1205963and 1205729
(37)
Results (37) are contained in the ring spanned by 1205991198943
1and
1205721198959
4
International Journal of Mathematics and Mathematical Sciences 5
4 119878119880(3) Prolongations
To formulate a 3 times 3 119878119880(3) problem the set of Pfaffianequations
120572119894= 0 120572
119894= 119889119910119894minus Ω119894119895119910119895 119894 119895 = 1 2 3 (38)
are associated with the nonlinear equation In (38) Ω is atraceless 3 times 3 matrix consisting of a system of one formsThe nonlinear equation to be considered is expressed as thevanishing of a traceless 3times3matrix of two formsΘ exactly asin (25) which constitute the integrability condition for (38)
A 3times3matrix representation of the Lie algebra for 119878119880(3) isintroduced by means of generators 120582
119895for 119895 = 1 8 which
satisfy the following set of commutation relations
[120582119897 120582119898] = 2119894 119891
119897119898119899120582119899 (39)
The structure constants 119891119897119898119899
are totally antisymmetric in119897 119898 119899The one formΩ is expressed in terms of the generators120582119894as
Ω =
8
sum
119897=1
120596119897120582119897 (40)
Then the two forms Θ can be written as
Θ =
8
sum
119897=1
120599119897120582119897 120599119897= 119889120596119897minus 119894119891119897119898119899
120596119898and 120596119899 (41)
The nonlinear equation to be solved has the form 120599119897= 0 for
119897 = 1 8It will be useful to display (40) and (41) by using the
nonzero structure constants given in (39) since thesemay notbe readily accessible An explicit representation for thematrixΩ used here is given by
Ω = (
1205963+
1
radic3
1205968
1205961minus 1198941205962
1205964minus 1198941205965
1205961+ 1198941205962
minus1205963+
1
radic3
12059681205966minus 1198941205967
1205964+ 1198941205965
1205966+ 1198941205967
minus2
radic3
1205968
) (42)
Moreover in order that the presentation can be easier tofollow the eight forms 119889120596
119894specified by (41) will be given
explicitly
1198891205961= 1205991+ 21198941205962and 1205963+ 1198941205964and 1205967minus 1198941205965and 1205966
1198891205962= 1205992minus 21198941205961and 1205963+ 1198941205964and 1205966+ 1198941205965and 1205967
1198891205963= 1205993+ 21198941205961and 1205962+ 1198941205964and 1205965minus 1198941205966and 1205967
1198891205964= 1205994minus 1198941205961and 1205967minus 1198941205962and 1205966minus 1198941205963and 1205965+ radic3119894120596
5and 1205968
1198891205965= 1205995+ 1198941205961and 1205966minus 1198941205962and 1205967+ 1198941205963and 1205964minus radic3119894120596
4and 1205968
1198891205966= 1205996minus 1198941205961and 1205965+ 1198941205962and 1205964+ 1198941205963and 1205967+ radic3119894120596
7and 1205968
1198891205967= 1205997+ 1198941205961and 1205964+ 1198941205962and 1205965minus 1198941205963and 1205966minus radic3119894120596
6and 1205968
1198891205968= 1205998+ radic3119894120596
4and 1205965+ radic3119894120596
6and 1205967
(43)
Substituting (42) into (38) the following system of one forms1205721198943
1is obtained
1205721= 1198891199101minus (1205963+
1
radic3
1205968)1199101minus (1205961minus 1198941205962) 1199102minus (1205964minus 1198941205965) 1199103
1205722= 1198891199102minus (1205961+ 1198941205962) 1199101+ (1205963minus
1
radic3
1205968)1199102minus (1205966minus 1198941205967) 1199103
1205723= 1198891199103minus (1205964+ 1198941205965) 1199101minus (1205966+ 1198941205967) 1199102+
2
radic3
12059681199103
(44)
The increase in complexity of this system makes it oftennecessary to resort to the use of symbolic manipulation tocarry out longer calculations and for the most part onlyresults are given
Theorem10 Theexterior derivatives of the120572119894in (44) are given
by
1198891205721= minus 119910
2(1205991minus 1198941205992) minus 11991011205993minus 1199103(1205994minus 1198941205995)
minus1
radic3
11991011205998+ (1205963+
1
radic3
1205968) and 1205721
+ (1205961minus 1198941205962) and 1205722+ (1205964minus 1198941205965) and 1205723
1198891205722= minus 119910
1(1205991+ 1198941205992) + 11991021205993
minus1
radic3
11991021205998minus 1199103(1205996minus 1198941205997) + (120596
1+ 1198941205962) and 1205721
minus (1205963minus
1
radic3
1205968) and 1205722+ (1205966minus 1198941205967) and 1205723
1198891205723= minus 119910
1(1205994+ 1198941205995) minus 1199102(1205996+ 1198941205997)
+2
radic3
11991031205998+ (1205964+ 1198941205965) and 1205721
+ (1205966+ 1198941205967) and 1205722minus
2
radic3
1205968and 1205723
(45)
In order to keep the notation concise an abbreviation willbe introduced Suppose that 120574
119894 is a system of forms and 119894 119895
are integers then we make the abbreviation
120574119894119895plusmn
= 120574119894plusmn 119894120574119895 (46)
At this point quadratic pseudopotentials can be introducedin terms of the homogeneous variables of the same form as
6 International Journal of Mathematics and Mathematical Sciences
(30) In the same way that (31) was produced the followingPfaffian equations based on the set 120572
1198943
1in (44) are obtained
1205724= 1198891199104minus 12059612+
+ 211991041205963+ 1199102
412059612minus
minus 119910512059667minus
+ 1199104119910512059645minus
1205725= 1198891199105minus 12059645+
+ 1199105(1205963+ radic3120596
8)
+ 1199102
512059645minus
minus 119910412059667+
+ 1199104119910512059612minus
1205726= 1198891199106minus 12059612minus
minus 211991061205963+ 1199102
612059612+
minus 119910712059645minus
+ 1199106119910712059667minus
1205727= 1198891199107minus 12059667+
minus 1199107(1205963minus radic3120596
8)
+ 1199102
712059667minus
minus 119910612059645+
+ 1199106119910712059612+
1205728= 1198891199108minus 12059645minus
minus 1199108(1205963+ radic3120596
8)
+ 1199102
812059645+
minus 119910912059612minus
+ 1199108119910912059667+
1205729= 1198891199109minus 12059667minus
+ 1199109(1205963minus radic3120596
8)
+ 1199102
912059667+
minus 119910812059612+
+ 1199108119910912059645+
(47)
These are coupledRiccati equations for the pairs of pseudopo-tentials (119910
4 1199105) (1199106 1199107) and (119910
8 1199109) respectively
Define the following set of 2 times 2matrices of one formsΩ119894
for 119894 = 1 2 3 as
Ω1=(minus21205963minus2119910412059612minusminus119910512059645minus 12059667minusminus119910412059645minus
12059667+minus119910512059612minus minus1205963minusradic31205968minus119910412059612minusminus2119910512059645minus
)
Ω2=(21205963minus2119910612059612+ minus 119910712059667minus 12059645minusminus119910612059667minus
12059645+minus119910712059612+ 1205963minusradic31205968minus119910612059612+minus2119910712059667minus
)
Ω3=(1205963+radic31205968minus2119910812059645+minus119910912059667+ 12059612minusminus119910812059667+
12059612+minus119910912059645+ minus1205963+radic31205968minus119910812059645+minus2119910912059667+
)
(48)
Making use of the matrices Ω119894defined in (48) the following
result can be stated
Theorem 11 The closure properties of the set of forms 1205721198949
4
given by (47) can be expressed in terms of the Ω119894as follows
119889(12057241205725)
= ((1199102
4minus 1) 1205991minus119894 (119910
2
4+ 1) 1205992+211991041205993+1199104119910512059945minusminus119910512059967minus
1199104119910512059912minus+11991051205993+(1199102
4minus 1) 1205994minus119894 (119910
2
5+ 1) 1205995minus119910412059967++
radic311991051205998
)
+Ω1 and (12057241205725)
119889 (12057261205727)
= ((1199102
6minus 1) 1205991+119894 (119910
2
6+ 1) 1205992minus211991061205993minus119910712059945minus+1199106119910712059967minus
1199106119910712059912+minus11991071205993minus119910612059945++(1199102
7minus 1) 1205996minus119894 (119910
2
7+ 1) 1205997+
radic311991071205998
)
+Ω2 and (12057261205727)
119889 (12057281205729)
= (minus119910912059912minusminus11991081205993+(119910
2
8minus 1) 1205994+119894 (119910
2
8+ 1) 1205995+1199108119910912059967+minus
radic311991081205998
minus119910812059912++11991091205993+1199108119910912059945++(1199102
9minus 1) 1205996+119894 (119910
2
9+ 1) 1205997minus
radic311991091205998
)
+Ω3 and (12057281205729)
(49)
Based on the forms Ω119894given in (48) we can differentiate
to define the following matrices of two forms 120585119894given by
120585119894= 119889Ω119894minus Ω119894and Ω119894 (50)
Theorem 12 The forms 120585119894defined in (50) are given explicitly
by the matrices
1205851
=(
212059612+ and 1205724+12059645minus and 1205725 12059645minus and 1205724minus119910412059945minus+12059967minus
minus2119910412059912minus minus 21205993 minus 119910512059945minus12059612minus and 1205724+212059645minus and 1205725
12059612minus and 1205725minus119910512059912minus+12059967+ minus119910412059912minusminus1205993 minus 212059945minus minusradic31205998
)
1205852
=(
212059612+ and 1205726+12059667minus and 1205727 12059667minus and 1205726+12059945minus minus 119910612059967minus
minus2119910612059912+ + 1205993 minus 119910712059967minus12059612+ and 1205726+212059667minus and 1205727minus119910612059912+
12059612+ and 1205727 minus 1199107 12059912+ + 12059945+ +1205993 minus 2119910712059967minus minusradic31205998
)
1205853
=(
212059645+ and 1205728+12059667+ and 1205729+1205993 12059667+ and 1205728+12059912minusminus119910812059967+
minus2119910812059945+ minus 119910912059967+ +radic3120599812059645+ and 1205728+212059667+ and 1205729minus1205993
12059645+ and 1205729+12059912+minus119910912059945+ minus119910812059945+ minus 2119910912059967+ +radic31205998
)
(51)
From these results it is concluded that 1205851is contained in
the ring of 1205724 1205725 and the 120599
119897 1205852is contained in the ring of
1205726 1205727 and 120599
119897 and 120585
3is in the ring of 120572
8 1205729 and 120599
119897
The two forms 1205851198943
1therefore vanish for the solutions of the
nonlinear equations (39) and of the coupled Riccati equations120572119895= 09
4 As in the case of 119874(3) the one forms Ω
119894are not
traceless Denoting the trace of Ω119894by
120591119894= trΩ
119894 (52)
the following theorem then follows
Theorem 13 The closure properties of the exterior derivativesof the traces 120591
119894are given by
1
31198891205911= 12059612minus
and 1205724+ 12059645minus
and 1205725
minus 119910412059912minus
minus 1205993minus 119910512059945minus
minus1
radic3
1205998
International Journal of Mathematics and Mathematical Sciences 7
1
31198891205912= 12059612+
and 1205726+ 12059667minus
and 1205727
minus 119910612059912+
+ 1205993minus 119910712059967minus
minus1
radic3
1205998
1
31198891205913= 12059645+
and 1205728+ 12059667+
and 1205729
minus 119910812059945+
minus 119910912059967+
+2
radic3
1205998
(53)
The one forms (52) then can be used to generate con-servation laws Note that as in the 119874(3) case a 3 times 3
problemΩ has been reduced to three separate 2times2 problemsin terms of the matrices Ω
119897 Further prolongation can be
continued beginning with the one formsΩ119897given in (48) To
briefly outline the further steps in the procedure a system ofPfaffians
119897119895 is introduced which are based on the one forms
Ω119897
119897119895= 0
119897119895= 119889119910119897119895minus (Ω119897)119895119896119910119897119896 (54)
The subscript 119897 in 119910119897119895and
119897119895indicates that they belong to the
subsystem defined byΩ119897 and it is not summed over Exterior
differentiation of 119897119895yields
119889119897119895= (Ω119897)119895119896and 119897119896minus (Θ)
119895119896119910119897119896 (55)
The 119910119897119895 are pseudopotentials for the original nonlinear
equation (39) Next quadratic pseudopotentials are includedas the homogeneous variables and the prolongation can becontinued
5 A Conservation Law and Summary
These types of results turn out to be very useful for furtherstudy of integrable equationsThey can be used for generatinginfinite numbers of conservation laws In addition the resultsare independent of any further structure of the forms 120596
119894in
all cases In fact the one form Ω need not be thought of asuniqueThis is due to the fact thatΩ andΘ are form invariantunder the gauge transformationΩ rarr 120596
1015840= 119889119860 119860
minus1+119860Ω119860
minus1
and Θ rarr Θ1015840= 119860Θ119860
minus1 where in the 119878119871(2R) case 119860 is anarbitrary 2 times 2 space-time-dependent matrix of determinantone The gauge transformation property holds in the 3 times 3
case as well The pseudopotentials serve as potentials forconservation laws in a generalized senseThey can be definedunder a choice of Pfaffian forms such as
120572119894= 0 120572
119894= 119889119910119894+ 119865119894119889119909 + 119866
119894119889119905 (56)
with the property that the exterior derivatives 119889120572119894are con-
tained in the ring spanned by 120572119894 and 120599
119897
119889120572119894= sum
119895
119860119894119895and 120572119895+sum
119897
Γ119894119897120599119897 (57)
This can be thought of as a generalization of the FrobeniusTheorem for complete integrability of Pfaffian systems
Theorem 3 implies that 119889120590119894= 0when 119894 = 1 2 for solutions
of the original equation If either of these forms is expressedas 120590 = I119889119909 +J119889119905 then 119889120590 = 0 implies that
120597I
120597119905minus120597J
120597119905= 0 (58)
ThusI is a conserved density andJ a conserved current Letus finally represent 120596
1= 1198861119889119909 + 119887
1119889119905 1205962= 1198862119889119909 + 119887
2119889119905 and
1205963= 120578119889119909 + 119887
3119889119905 where 120578 is a parameter The 119909-dependent
piece of 1205723in (17) implies
1199103119909
+ 211988611199103+ 11988621199102
3minus 120578 = 0 (59)
By substituting an asymptotic expansion around 120578 = infin for1199103in (59) of the form
1199103=
infin
sum
0
120578minus119899119884119899 (60)
a recursion for the 119884119899is obtained Thus (59) becomes
sum
119899
120578minus119899119884119899119909
+ 21198861sum
119899
120578minus119899119884119899
+ 1198862(sum
119899
120578minus119899119884119899)
2
minus 120578 = 0
(61)
Expanding the power collecting coefficients of 120578 and equat-ing coefficients of 120578 to zero we get
1198841119909
+ 211988611198841= 1 119884
119899119909+ 21198861119884119899+ 1198862
119899minus1
sum
119896=1
119884119899minus119896
119884119896= 0
(62)
The consistency of solving 1205723by using just the 119909 part is
guaranteed by complete integrability The 119909 part of the form1205901is expressed as
(1205901)119909= (1198861+
infin
sum
119899=1
120578minus1198991198841198991198862)119889119909 (63)
Consequently from (58) the 119899th conserved density is
I119899= 1198862119884119899 (64)
The existence of links between the types of prolongationhere and other types of prolongations which are based onclosed differential systems is a subject for further work
References
[1] F B Estabrook and H D Wahlquist ldquoClassical geometriesdefined by exterior differential systems on higher frame bun-dlesrdquo Classical and Quantum Gravity vol 6 no 3 pp 263ndash2741989
[2] H Cartan Differential Forms Dover Mineola NY USA 2006[3] M J Ablowitz D J Kaup A C Newell and H Segur ldquoMethod
for solving the sine-Gordon equationrdquo Physical Review Lettersvol 30 pp 1262ndash1264 1973
8 International Journal of Mathematics and Mathematical Sciences
[4] M J Ablowitz D K Kaup A C Newell and H SegurldquoNonlinear-evolution equations of physical significancerdquo Phys-ical Review Letters vol 31 pp 125ndash127 1973
[5] R Sasaki ldquoPseudopotentials for the general AKNS systemrdquoPhysics Letters A vol 73 no 2 pp 77ndash80 1979
[6] R Sasaki ldquoGeometric approach to soliton equationsrdquo Proceed-ings of the Royal Society London vol 373 no 1754 pp 373ndash3841980
[7] M Crampin ldquoSolitons and 119878119871(2R)rdquo Physics Letters A vol 66no 3 pp 170ndash172 1978
[8] D J Kaup and J Yang ldquoThe inverse scattering transform andsquared eigenfunctions for a degenerate 3 times 3 operatorrdquo InverseProblems vol 25 no 10 Article ID 105010 2009
[9] D J Kaup and R A Van Gorder ldquoThe inverse scatteringtransform and squared eigenfunctions for the nondegenerate3 times 3 operator and its soliton structurerdquo Inverse Problems vol26 no 5 Article ID 055005 2010
[10] P Bracken ldquoIntrinsic formulation of geometric integrabilityand associated Riccati system generating conservation lawsrdquoInternational Journal of Geometric Methods in Modern Physicsvol 6 no 5 pp 825ndash837 2009
[11] D J Kaup and R A Van Gorder ldquoSquared eigenfunctions andthe perturbation theory for the nondegenerate N timesN operatora general outlinerdquo Journal of Physics A vol 43 Article ID434019 2010
[12] H D Wahlquist and F B Estabrook ldquoProlongation structuresof nonlinear evolution equationsrdquo Journal of MathematicalPhysics vol 16 pp 1ndash7 1975
[13] P Bracken ldquoOn two-dimensional manifolds with constantGaussian curvature and their associated equationsrdquo Interna-tional Journal of Geometric Methods in Modern Physics vol 9no 3 Article ID 1250018 2012
Submit your manuscripts athttpwwwhindawicom
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Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
2 International Journal of Mathematics and Mathematical Sciences
the end a collection of conservation laws are developed fromone of the results and some speculation as to how this typerelates to other procedures [12 13]
2 119878119871(2R) Prolongations
The procedure begins by associating a system of Pfaffianequations to the nonlinear system to be studied namely
120572119894= 0 120572
119894= 119889119910119894minus Ω119894119895119910119895 119894 119895 = 1 2 (1)
In (1) Ω is a traceless 2 times 2 matrix which consists of afamily of one forms 120596
119894 At the end it is desired to express
these one forms in terms of independent variables which arecalled 119909 and 119905 the dependent variables and their derivativesHowever no specific equation need be assumed at the startThe underlying structure group is 119878119871(2R) Explicitly thematrix of one forms is given by the 2 times 2matrix
Ω = (1205961
1205962
1205963minus1205961
) (2)
The integrability conditions are expressed as the vanishing ofa traceless 2 times 2matrix of two forms Θ given by
Θ = 119889Ω minus Ω and Ω (3)
In terms of components the left-hand side of (3) has the form
Θ = (Θ119894119895) = (
1205991
1205992
1205993minus1205991
) (4)
Substituting (2) into (3) a matrix which contains the integra-bility equations in terms of the basis one forms is obtainedThe three equations are
1205991= 1198891205961minus 1205962and 1205963 120599
2= 1198891205962minus 21205961and 1205962
1205993= 1198891205963+ 21205961and 1205963
(5)
Of use in the theorems which follow it is also useful to havethe 119889120596
119894in (5) expressed explicitly in terms of the 120599
119894as
1198891205961= 1205991+ 1205962and 1205963 119889120596
2= 1205992+ 21205961and 1205962
1198891205963= 1205993minus 21205961and 1205963
(6)
Therefore by selecting a particular choice for the set 120596119894 the
nonlinear equation of interest can be written simply as
Θ = 0 120599119894= 0 119894 = 1 2 3 (7)
It is easy to see that the system is closed Upon differentiatingΘ and substituting (3) we obtain
119889Θ = Ω and Θ minus Θ and Ω (8)
This implies that the exterior derivatives of the set of 120599119894 are
contained in the ring of two forms 120599119894
Now the differential ideal can be prolonged by includingthe forms 120572
1 1205722 given by (1)
Theorem 1 The differential one forms
1205721= 1198891199101minus 12059611199101minus 12059621199102 120572
2= 1198891199102minus 12059631199101+ 12059611199102 (9)
have the following exterior derivatives
1198891205721= 1205961and 1205721+ 1205962and 1205722minus 11991011205991minus 11991021205992
1198891205722= minus 120596
1and 1205722+ 1205963and 1205721+ 11991021205991minus 11991011205993
(10)
Hence the exterior derivatives of the 120572119894 are contained in the
ring of forms 120599119894 120572119895
Proof The forms (9) follow by substituting (2) into (1)Differentiating 120572
1in (9) it is found that
1198891205721= minus11991011198891205961+ 1205961and 1198891199101minus 11991021198891205962+ 1205962and 1198891199102 (11)
Obtaining 1198891199101and 119889119910
2from (9) and 119889120596
1 1198891205962from (6) 119889120572
1
becomes
1198891205721= minus11991011205991minus 11991011205962and 1205963+ 1205961and 1205721+ 11991021205961and 1205962minus 11991021205992
minus 211991021205961and 1205962+ 1205962and 1205722+ 11991011205962and 1205963minus 11991021205962and 1205961
= 1205961and 1205721+ 1205962and 1205722minus 11991011205991minus 11991021205992
(12)
Similarly beginning with 1205722
1198891205722= minus11991011198891205963+ 1205963and 1198891199101+ 11991021198891205961minus 1205961and 1198891199102
= minus11991011205993+ 211991011205961and 1205963+ 1205963and 1205721
+ 11991011205963and 1205961+ 11991021205963and 1205962
+ 11991021205991+ 11991021205962and 1205963minus 1205961and 1205722minus 11991011205961and 1205963
= minus1205961and 1205722+ 1205963and 1205721+ 11991021205991minus 11991011205993
(13)
as required
Corollary 2 The exterior derivatives of the 120572119894in (9) can be
expressed concisely in terms of the matrix elements ofΘ andΩas
119889120572119894= minusΘ119894119895119910119895+ Ω119894119895and 120572119895 119894 119895 = 1 2 (14)
The corollary is Theorem 1 after using the definitions ofthe matrices in (2) and (4)
The forms 1205721 1205722given in (9) lead to a natural Riccati
representation called 1205723 1205724for this differential system This
arises by taking the following linear combinations of 1205721and
1205722
1199102
11205723= 11991011205722minus 11991021205721
= 11991011198891199102minus 11991021198891199101minus 1199102
11205963+ 2119910111991021205961+ 1199102
21205962
1199102
21205724= 11991021205721minus 11991011205722
= 11991021198891199101minus 11991011198891199102minus 1199102
21205962minus 2119910111991021205961+ 1199102
11205963
(15)
International Journal of Mathematics and Mathematical Sciences 3
Two new functions or pseudopotentials 1199103and 119910
4can be
introduced which are defined by the transformation
1199103=1199102
1199101
1199104=1199101
1199102
(16)
Then from (15) the following forms which have a Riccatistructure result
1205723= 1198891199103minus 1205963+ 211991031205961+ 1199102
31205962
1205724= 1198891199104minus 1205962minus 211991041205961+ 1199102
41205963
(17)
These equations could also be thought of as Riccati equationsfor 1199103and 119910
4
Theorem3 (i)Theone forms12057231205724given by (17) have exterior
derivatives
1198891205723= 211991031205991+ 1199102
31205992minus 1205993+ 21205723and (1205961+ 11991031205962)
1198891205724= minus 2119910
41205991minus 1205992+ 1199102
41205993+ 21205724and (minus120596
1+ 11991041205963)
(18)
Consequently results (18) are contained in the ring spanned by120599119894 and 120572
119895
(ii) Define the forms 1205901= 1205961+ 11991031205962and 120590
2= minus120596
1+
11991041205963appearing in (18) The exterior derivatives of 120590
1and 120590
2
are found to be
1198891205901= 1205991+ 11991031205992+ 1205723and 1205962
1198891205902= minus1205991+ 11991031205992+ 1205724and 1205962
(19)
Therefore 1198891205901equiv 0 and 119889120590
2equiv 0 mod 120599
119894 120572119895
The proof of this Theorem proceeds along exactly thesame lines as Theorem 1 The 119878119871(2R) structure and theconnection interpretation can be based on the forms 120572
3 1205724
At this point the process can be continued Two morepseudopotentials 119910
5and 119910
6can be introduced and the
differential system can be extended by including two moreone forms 120572
5and 120572
6 The specific structure of these forms is
suggested byTheorem 3
Theorem 4 Define two one forms 1205725and 120572
6as
1205725= 1198891199105minus 1205961minus 11991031205962 120572
6= 1198891199106+ 1205961minus 11991041205963 (20)
The exterior derivatives of the one forms (20) are given by theexpressions
1198891205725= minus1205991minus 11991031205993minus 1205723and 1205962 119889120572
6= 1205991minus 11991041205993minus 1205724and 1205963
(21)
Results (21) specify the closure properties of the forms 1205725and
1205726 This theorem is proved along similar lines keeping in mind
that the results for 1198891199103and 119889119910
4are obtained from (17)
A final extension can be made by adding two additionalpseudopotentials119910
7and1199108 At each stage the ideal of forms is
being enlarged and is found to be closed over the underlyingsubideal which does not contain the two new forms
Theorem 5 Define the one forms 1205727and 120572
8by means of
1205727= 1198891199107minus 119890minus211991051205962 120572
8= 1198891199108minus 119890minus211991061205963 (22)
The exterior derivatives of the forms 1205727and 120572
8are given by
1198891205727= 2119890minus211991051205725and 1205962minus 119890minus211991051205992
1198891205728= 2119890minus211991061205726and 1205963minus 119890minus211991061205993
(23)
and are closed over the prolonged ideal
3 119874(3) Prolongations
The first 3 times 3 problem we consider is formulated in terms ofa set of one forms 120596
119894for 119894 = 1 2 3 The following system of
Pfaffian equations is to be associated to a specific nonlinearequation
120572119894= 0 120572
119894= 119889119910119894minus Ω119894119895119910119895 119894 119895 = 1 2 3 (24)
In (24) Ω is a traceless 3 times 3 matrix of one forms Thenonlinear equation to emerge is expressed as the vanishingof a traceless 3 times 3matrix of two forms Θ
Θ = 0 Θ = 119889Ω minus Ω and Ω (25)These can be considered as integrability conditions for (24)The closure property the gauge transformation and the gaugetheoretic interpretation can also hold for 3 times 3 systemsExplicitly the matrixΩ is given by
Ω = (
0 minus1205961
1205962
1205961
0 minus1205963
minus1205962
1205963
0
) (26)
Using (26) in (24) and (25) the following prolonged differen-tial system is obtained
1198891199101= 1205721minus 11991021205961+ 11991031205962 119889120596
1= 1205991minus 1205962and 1205963
1198891199102= 1205722+ 11991011205961minus 11991031205963 119889120596
2= 1205992minus 1205963and 1205961
1198891199103= 1205723minus 11991011205962+ 11991021205963 119889120596
3= 1205993minus 1205961and 1205962
(27)
By straightforward exterior differentiation of each 120572119894and
using (27) the followingTheorem results
Theorem 6 The 120572119894given in (27) have exterior derivatives
which are contained in the ring spanned by 1205991198943
1and 120572
1198953
1and
given explicitly as1198891205721= 11991021205991minus 11991031205992minus 1205961and 1205722+ 1205962and 1205723
1198891205722= minus 119910
11205991+ 11991031205993+ 1205961and 1205721minus 1205963and 1205723
1198891205723= 11991011205992minus 11991021205993minus 1205962and 1205721+ 1205963and 1205722
(28)
The one forms 1205721198943
1admit a series of Riccati representa-
tions which can be realized by defining six new one forms
1199102
11205724= 11991011205722minus 11991021205721 119910
2
11205725= 11991011205723minus 11991031205721
1199102
21205726= 11991021205721minus 11991011205722
1199102
21205727= 11991021205723minus 11991031205722 119910
2
31205728= 11991031205721minus 11991011205723
1199102
31205729= 11991031205722minus 11991021205723
(29)
4 International Journal of Mathematics and Mathematical Sciences
In effect the larger 3times3 system is breaking up into several 2times2systems To write the new one forms explicitly introduce thenew functions 119910
1198959
4which are defined in terms of the original
1199101198943
1as follows
1199104=1199102
1199101
1199105=1199103
1199101
1199106=1199101
1199102
1199107=1199103
1199101
1199108=1199101
1199103
1199109=1199102
1199103
(30)
In terms of the functions defined in (30) the 1205721198959
4are given
as
1205724= 1198891199104minus (1 + 119910
2
4) 1205961+ 119910411991051205962+ 11991051205963
1205725= 1198891199105minus 119910411991051205961+ (1 + 119910
2
5) 1205962minus 11991041205963
1205726= 1198891199106+ (1 + 119910
2
6) 1205961minus 11991071205962minus 119910611991071205963
1205727= 1198891199107+ 119910611991071205961+ 11991061205962minus (1 + 119910
2
7) 1205963
1205728= 1198891199108+ 11991091205961minus (1 + 119910
2
8) 1205962+ 119910811991091205963
1205729= 1198891199109minus 11991081205961minus 119910811991091205962+ (1 + 119910
2
9) 1205963
(31)
To state the next theorem we need to define the followingthree matrices
Ω1= (
211991041205961minus 11991051205962
minus11991041205962minus 1205963
11991051205961+ 1205963
11991041205961minus 211991051205962
)
Ω2= (
minus211991061205961+ 11991071205963
1205962+ 11991061205963
minus11991071205961minus 1205966
minus11991061205961+ 211991071205963
)
Ω3= (
211991081205962minus 11991091205963
minus1205961minus 11991091205963
1205961+ 11991091205962
11991081205962minus 211991091205963
)
(32)
Theorem 7 The closure properties for the forms 1205721198949
4given in
(31) can be summarized in the form
119889(1205724
1205725
) = (minus (1 + 119910
2
4) 1205991+ 119910411991051205992+ 11991051205993
minus119910411991051205991+ (1 + 119910
2
5) 1205992minus 11991041205993
)
+ Ω1and (
1205724
1205725
)
119889 (1205726
1205727
) = ((1 + 119910
2
6) 1205991minus 11991071205992minus 119910611991071205993
119910611991071205991+ 11991061205992minus (1 + 119910
2
7) 1205993
)
+ Ω2and (
1205726
1205727
)
119889 (1205728
1205729
) = (11991011205991minus (1 + 119910
2
8) 1205992+ 119910811991091205993
minus11991081205991minus 119910811991091205992+ (1 + 119910
2
9) 1205993
)
+ Ω3and (
1205728
1205729
)
(33)
The exterior derivatives are therefore contained in the ringspanned by 120599
1198943
1and the 120572
1198959
4
In terms of Ω119894 a corresponding matrix of two forms Θ
119894
can be defined in terms of the corresponding Ω119894defined in
(32)
Θ119894= 119889Ω119894minus Ω119894and Ω119894 119894 = 1 2 3 (34)
Theorem 8 The 2 times 2matrix of two forms Θ119894defined by (34)
is contained in the ring of forms spanned by 1205991198943
1coupled with
either 1205724 1205725 1205726 1205727 or 120572
8 1205729when 119894 = 1 2 3 respectively
Proof DifferentiatingΩ1and simplifying we have
Θ1= 119889Ω1minus Ω1and Ω1
= (211991041205991minus 11991051205992+ 21205724and 1205961minus 1205725and 1205962
minus11991041205992minus 1205993minus 1205724and 1205962
11991051205991+ 1205993+ 1205725and 1205961
11991041205991minus 211991051205992+ 1205724and 1205961minus 21205725and 1205962
)
(35)
Similarmatrix expressions can be found for the cases inwhichΩ1is replaced by Ω
2orΩ3 respectively
Unlike Ω given in (26) the Ω119894in (32) are not traceless
Define their traces to be
120581119894= trΩ
119894 119894 = 1 2 3 (36)
These traces provide convenient ways of generating conser-vation laws on account of the followingTheorem
Theorem 9 The exterior derivatives of traces (36) are given by
1
31198891205811= 11991041205991minus 11991051205992minus 1205961and 1205724+ 1205962and 1205725
1
31198891205812= minus 119910
61205991+ 11991071205993+ 1205961and 1205726minus 1205963and 1205727
1
31198891205813= 11991081205992minus 11991091205993minus 1205962and 1205728+ 1205963and 1205729
(37)
Results (37) are contained in the ring spanned by 1205991198943
1and
1205721198959
4
International Journal of Mathematics and Mathematical Sciences 5
4 119878119880(3) Prolongations
To formulate a 3 times 3 119878119880(3) problem the set of Pfaffianequations
120572119894= 0 120572
119894= 119889119910119894minus Ω119894119895119910119895 119894 119895 = 1 2 3 (38)
are associated with the nonlinear equation In (38) Ω is atraceless 3 times 3 matrix consisting of a system of one formsThe nonlinear equation to be considered is expressed as thevanishing of a traceless 3times3matrix of two formsΘ exactly asin (25) which constitute the integrability condition for (38)
A 3times3matrix representation of the Lie algebra for 119878119880(3) isintroduced by means of generators 120582
119895for 119895 = 1 8 which
satisfy the following set of commutation relations
[120582119897 120582119898] = 2119894 119891
119897119898119899120582119899 (39)
The structure constants 119891119897119898119899
are totally antisymmetric in119897 119898 119899The one formΩ is expressed in terms of the generators120582119894as
Ω =
8
sum
119897=1
120596119897120582119897 (40)
Then the two forms Θ can be written as
Θ =
8
sum
119897=1
120599119897120582119897 120599119897= 119889120596119897minus 119894119891119897119898119899
120596119898and 120596119899 (41)
The nonlinear equation to be solved has the form 120599119897= 0 for
119897 = 1 8It will be useful to display (40) and (41) by using the
nonzero structure constants given in (39) since thesemay notbe readily accessible An explicit representation for thematrixΩ used here is given by
Ω = (
1205963+
1
radic3
1205968
1205961minus 1198941205962
1205964minus 1198941205965
1205961+ 1198941205962
minus1205963+
1
radic3
12059681205966minus 1198941205967
1205964+ 1198941205965
1205966+ 1198941205967
minus2
radic3
1205968
) (42)
Moreover in order that the presentation can be easier tofollow the eight forms 119889120596
119894specified by (41) will be given
explicitly
1198891205961= 1205991+ 21198941205962and 1205963+ 1198941205964and 1205967minus 1198941205965and 1205966
1198891205962= 1205992minus 21198941205961and 1205963+ 1198941205964and 1205966+ 1198941205965and 1205967
1198891205963= 1205993+ 21198941205961and 1205962+ 1198941205964and 1205965minus 1198941205966and 1205967
1198891205964= 1205994minus 1198941205961and 1205967minus 1198941205962and 1205966minus 1198941205963and 1205965+ radic3119894120596
5and 1205968
1198891205965= 1205995+ 1198941205961and 1205966minus 1198941205962and 1205967+ 1198941205963and 1205964minus radic3119894120596
4and 1205968
1198891205966= 1205996minus 1198941205961and 1205965+ 1198941205962and 1205964+ 1198941205963and 1205967+ radic3119894120596
7and 1205968
1198891205967= 1205997+ 1198941205961and 1205964+ 1198941205962and 1205965minus 1198941205963and 1205966minus radic3119894120596
6and 1205968
1198891205968= 1205998+ radic3119894120596
4and 1205965+ radic3119894120596
6and 1205967
(43)
Substituting (42) into (38) the following system of one forms1205721198943
1is obtained
1205721= 1198891199101minus (1205963+
1
radic3
1205968)1199101minus (1205961minus 1198941205962) 1199102minus (1205964minus 1198941205965) 1199103
1205722= 1198891199102minus (1205961+ 1198941205962) 1199101+ (1205963minus
1
radic3
1205968)1199102minus (1205966minus 1198941205967) 1199103
1205723= 1198891199103minus (1205964+ 1198941205965) 1199101minus (1205966+ 1198941205967) 1199102+
2
radic3
12059681199103
(44)
The increase in complexity of this system makes it oftennecessary to resort to the use of symbolic manipulation tocarry out longer calculations and for the most part onlyresults are given
Theorem10 Theexterior derivatives of the120572119894in (44) are given
by
1198891205721= minus 119910
2(1205991minus 1198941205992) minus 11991011205993minus 1199103(1205994minus 1198941205995)
minus1
radic3
11991011205998+ (1205963+
1
radic3
1205968) and 1205721
+ (1205961minus 1198941205962) and 1205722+ (1205964minus 1198941205965) and 1205723
1198891205722= minus 119910
1(1205991+ 1198941205992) + 11991021205993
minus1
radic3
11991021205998minus 1199103(1205996minus 1198941205997) + (120596
1+ 1198941205962) and 1205721
minus (1205963minus
1
radic3
1205968) and 1205722+ (1205966minus 1198941205967) and 1205723
1198891205723= minus 119910
1(1205994+ 1198941205995) minus 1199102(1205996+ 1198941205997)
+2
radic3
11991031205998+ (1205964+ 1198941205965) and 1205721
+ (1205966+ 1198941205967) and 1205722minus
2
radic3
1205968and 1205723
(45)
In order to keep the notation concise an abbreviation willbe introduced Suppose that 120574
119894 is a system of forms and 119894 119895
are integers then we make the abbreviation
120574119894119895plusmn
= 120574119894plusmn 119894120574119895 (46)
At this point quadratic pseudopotentials can be introducedin terms of the homogeneous variables of the same form as
6 International Journal of Mathematics and Mathematical Sciences
(30) In the same way that (31) was produced the followingPfaffian equations based on the set 120572
1198943
1in (44) are obtained
1205724= 1198891199104minus 12059612+
+ 211991041205963+ 1199102
412059612minus
minus 119910512059667minus
+ 1199104119910512059645minus
1205725= 1198891199105minus 12059645+
+ 1199105(1205963+ radic3120596
8)
+ 1199102
512059645minus
minus 119910412059667+
+ 1199104119910512059612minus
1205726= 1198891199106minus 12059612minus
minus 211991061205963+ 1199102
612059612+
minus 119910712059645minus
+ 1199106119910712059667minus
1205727= 1198891199107minus 12059667+
minus 1199107(1205963minus radic3120596
8)
+ 1199102
712059667minus
minus 119910612059645+
+ 1199106119910712059612+
1205728= 1198891199108minus 12059645minus
minus 1199108(1205963+ radic3120596
8)
+ 1199102
812059645+
minus 119910912059612minus
+ 1199108119910912059667+
1205729= 1198891199109minus 12059667minus
+ 1199109(1205963minus radic3120596
8)
+ 1199102
912059667+
minus 119910812059612+
+ 1199108119910912059645+
(47)
These are coupledRiccati equations for the pairs of pseudopo-tentials (119910
4 1199105) (1199106 1199107) and (119910
8 1199109) respectively
Define the following set of 2 times 2matrices of one formsΩ119894
for 119894 = 1 2 3 as
Ω1=(minus21205963minus2119910412059612minusminus119910512059645minus 12059667minusminus119910412059645minus
12059667+minus119910512059612minus minus1205963minusradic31205968minus119910412059612minusminus2119910512059645minus
)
Ω2=(21205963minus2119910612059612+ minus 119910712059667minus 12059645minusminus119910612059667minus
12059645+minus119910712059612+ 1205963minusradic31205968minus119910612059612+minus2119910712059667minus
)
Ω3=(1205963+radic31205968minus2119910812059645+minus119910912059667+ 12059612minusminus119910812059667+
12059612+minus119910912059645+ minus1205963+radic31205968minus119910812059645+minus2119910912059667+
)
(48)
Making use of the matrices Ω119894defined in (48) the following
result can be stated
Theorem 11 The closure properties of the set of forms 1205721198949
4
given by (47) can be expressed in terms of the Ω119894as follows
119889(12057241205725)
= ((1199102
4minus 1) 1205991minus119894 (119910
2
4+ 1) 1205992+211991041205993+1199104119910512059945minusminus119910512059967minus
1199104119910512059912minus+11991051205993+(1199102
4minus 1) 1205994minus119894 (119910
2
5+ 1) 1205995minus119910412059967++
radic311991051205998
)
+Ω1 and (12057241205725)
119889 (12057261205727)
= ((1199102
6minus 1) 1205991+119894 (119910
2
6+ 1) 1205992minus211991061205993minus119910712059945minus+1199106119910712059967minus
1199106119910712059912+minus11991071205993minus119910612059945++(1199102
7minus 1) 1205996minus119894 (119910
2
7+ 1) 1205997+
radic311991071205998
)
+Ω2 and (12057261205727)
119889 (12057281205729)
= (minus119910912059912minusminus11991081205993+(119910
2
8minus 1) 1205994+119894 (119910
2
8+ 1) 1205995+1199108119910912059967+minus
radic311991081205998
minus119910812059912++11991091205993+1199108119910912059945++(1199102
9minus 1) 1205996+119894 (119910
2
9+ 1) 1205997minus
radic311991091205998
)
+Ω3 and (12057281205729)
(49)
Based on the forms Ω119894given in (48) we can differentiate
to define the following matrices of two forms 120585119894given by
120585119894= 119889Ω119894minus Ω119894and Ω119894 (50)
Theorem 12 The forms 120585119894defined in (50) are given explicitly
by the matrices
1205851
=(
212059612+ and 1205724+12059645minus and 1205725 12059645minus and 1205724minus119910412059945minus+12059967minus
minus2119910412059912minus minus 21205993 minus 119910512059945minus12059612minus and 1205724+212059645minus and 1205725
12059612minus and 1205725minus119910512059912minus+12059967+ minus119910412059912minusminus1205993 minus 212059945minus minusradic31205998
)
1205852
=(
212059612+ and 1205726+12059667minus and 1205727 12059667minus and 1205726+12059945minus minus 119910612059967minus
minus2119910612059912+ + 1205993 minus 119910712059967minus12059612+ and 1205726+212059667minus and 1205727minus119910612059912+
12059612+ and 1205727 minus 1199107 12059912+ + 12059945+ +1205993 minus 2119910712059967minus minusradic31205998
)
1205853
=(
212059645+ and 1205728+12059667+ and 1205729+1205993 12059667+ and 1205728+12059912minusminus119910812059967+
minus2119910812059945+ minus 119910912059967+ +radic3120599812059645+ and 1205728+212059667+ and 1205729minus1205993
12059645+ and 1205729+12059912+minus119910912059945+ minus119910812059945+ minus 2119910912059967+ +radic31205998
)
(51)
From these results it is concluded that 1205851is contained in
the ring of 1205724 1205725 and the 120599
119897 1205852is contained in the ring of
1205726 1205727 and 120599
119897 and 120585
3is in the ring of 120572
8 1205729 and 120599
119897
The two forms 1205851198943
1therefore vanish for the solutions of the
nonlinear equations (39) and of the coupled Riccati equations120572119895= 09
4 As in the case of 119874(3) the one forms Ω
119894are not
traceless Denoting the trace of Ω119894by
120591119894= trΩ
119894 (52)
the following theorem then follows
Theorem 13 The closure properties of the exterior derivativesof the traces 120591
119894are given by
1
31198891205911= 12059612minus
and 1205724+ 12059645minus
and 1205725
minus 119910412059912minus
minus 1205993minus 119910512059945minus
minus1
radic3
1205998
International Journal of Mathematics and Mathematical Sciences 7
1
31198891205912= 12059612+
and 1205726+ 12059667minus
and 1205727
minus 119910612059912+
+ 1205993minus 119910712059967minus
minus1
radic3
1205998
1
31198891205913= 12059645+
and 1205728+ 12059667+
and 1205729
minus 119910812059945+
minus 119910912059967+
+2
radic3
1205998
(53)
The one forms (52) then can be used to generate con-servation laws Note that as in the 119874(3) case a 3 times 3
problemΩ has been reduced to three separate 2times2 problemsin terms of the matrices Ω
119897 Further prolongation can be
continued beginning with the one formsΩ119897given in (48) To
briefly outline the further steps in the procedure a system ofPfaffians
119897119895 is introduced which are based on the one forms
Ω119897
119897119895= 0
119897119895= 119889119910119897119895minus (Ω119897)119895119896119910119897119896 (54)
The subscript 119897 in 119910119897119895and
119897119895indicates that they belong to the
subsystem defined byΩ119897 and it is not summed over Exterior
differentiation of 119897119895yields
119889119897119895= (Ω119897)119895119896and 119897119896minus (Θ)
119895119896119910119897119896 (55)
The 119910119897119895 are pseudopotentials for the original nonlinear
equation (39) Next quadratic pseudopotentials are includedas the homogeneous variables and the prolongation can becontinued
5 A Conservation Law and Summary
These types of results turn out to be very useful for furtherstudy of integrable equationsThey can be used for generatinginfinite numbers of conservation laws In addition the resultsare independent of any further structure of the forms 120596
119894in
all cases In fact the one form Ω need not be thought of asuniqueThis is due to the fact thatΩ andΘ are form invariantunder the gauge transformationΩ rarr 120596
1015840= 119889119860 119860
minus1+119860Ω119860
minus1
and Θ rarr Θ1015840= 119860Θ119860
minus1 where in the 119878119871(2R) case 119860 is anarbitrary 2 times 2 space-time-dependent matrix of determinantone The gauge transformation property holds in the 3 times 3
case as well The pseudopotentials serve as potentials forconservation laws in a generalized senseThey can be definedunder a choice of Pfaffian forms such as
120572119894= 0 120572
119894= 119889119910119894+ 119865119894119889119909 + 119866
119894119889119905 (56)
with the property that the exterior derivatives 119889120572119894are con-
tained in the ring spanned by 120572119894 and 120599
119897
119889120572119894= sum
119895
119860119894119895and 120572119895+sum
119897
Γ119894119897120599119897 (57)
This can be thought of as a generalization of the FrobeniusTheorem for complete integrability of Pfaffian systems
Theorem 3 implies that 119889120590119894= 0when 119894 = 1 2 for solutions
of the original equation If either of these forms is expressedas 120590 = I119889119909 +J119889119905 then 119889120590 = 0 implies that
120597I
120597119905minus120597J
120597119905= 0 (58)
ThusI is a conserved density andJ a conserved current Letus finally represent 120596
1= 1198861119889119909 + 119887
1119889119905 1205962= 1198862119889119909 + 119887
2119889119905 and
1205963= 120578119889119909 + 119887
3119889119905 where 120578 is a parameter The 119909-dependent
piece of 1205723in (17) implies
1199103119909
+ 211988611199103+ 11988621199102
3minus 120578 = 0 (59)
By substituting an asymptotic expansion around 120578 = infin for1199103in (59) of the form
1199103=
infin
sum
0
120578minus119899119884119899 (60)
a recursion for the 119884119899is obtained Thus (59) becomes
sum
119899
120578minus119899119884119899119909
+ 21198861sum
119899
120578minus119899119884119899
+ 1198862(sum
119899
120578minus119899119884119899)
2
minus 120578 = 0
(61)
Expanding the power collecting coefficients of 120578 and equat-ing coefficients of 120578 to zero we get
1198841119909
+ 211988611198841= 1 119884
119899119909+ 21198861119884119899+ 1198862
119899minus1
sum
119896=1
119884119899minus119896
119884119896= 0
(62)
The consistency of solving 1205723by using just the 119909 part is
guaranteed by complete integrability The 119909 part of the form1205901is expressed as
(1205901)119909= (1198861+
infin
sum
119899=1
120578minus1198991198841198991198862)119889119909 (63)
Consequently from (58) the 119899th conserved density is
I119899= 1198862119884119899 (64)
The existence of links between the types of prolongationhere and other types of prolongations which are based onclosed differential systems is a subject for further work
References
[1] F B Estabrook and H D Wahlquist ldquoClassical geometriesdefined by exterior differential systems on higher frame bun-dlesrdquo Classical and Quantum Gravity vol 6 no 3 pp 263ndash2741989
[2] H Cartan Differential Forms Dover Mineola NY USA 2006[3] M J Ablowitz D J Kaup A C Newell and H Segur ldquoMethod
for solving the sine-Gordon equationrdquo Physical Review Lettersvol 30 pp 1262ndash1264 1973
8 International Journal of Mathematics and Mathematical Sciences
[4] M J Ablowitz D K Kaup A C Newell and H SegurldquoNonlinear-evolution equations of physical significancerdquo Phys-ical Review Letters vol 31 pp 125ndash127 1973
[5] R Sasaki ldquoPseudopotentials for the general AKNS systemrdquoPhysics Letters A vol 73 no 2 pp 77ndash80 1979
[6] R Sasaki ldquoGeometric approach to soliton equationsrdquo Proceed-ings of the Royal Society London vol 373 no 1754 pp 373ndash3841980
[7] M Crampin ldquoSolitons and 119878119871(2R)rdquo Physics Letters A vol 66no 3 pp 170ndash172 1978
[8] D J Kaup and J Yang ldquoThe inverse scattering transform andsquared eigenfunctions for a degenerate 3 times 3 operatorrdquo InverseProblems vol 25 no 10 Article ID 105010 2009
[9] D J Kaup and R A Van Gorder ldquoThe inverse scatteringtransform and squared eigenfunctions for the nondegenerate3 times 3 operator and its soliton structurerdquo Inverse Problems vol26 no 5 Article ID 055005 2010
[10] P Bracken ldquoIntrinsic formulation of geometric integrabilityand associated Riccati system generating conservation lawsrdquoInternational Journal of Geometric Methods in Modern Physicsvol 6 no 5 pp 825ndash837 2009
[11] D J Kaup and R A Van Gorder ldquoSquared eigenfunctions andthe perturbation theory for the nondegenerate N timesN operatora general outlinerdquo Journal of Physics A vol 43 Article ID434019 2010
[12] H D Wahlquist and F B Estabrook ldquoProlongation structuresof nonlinear evolution equationsrdquo Journal of MathematicalPhysics vol 16 pp 1ndash7 1975
[13] P Bracken ldquoOn two-dimensional manifolds with constantGaussian curvature and their associated equationsrdquo Interna-tional Journal of Geometric Methods in Modern Physics vol 9no 3 Article ID 1250018 2012
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Stochastic AnalysisInternational Journal of
International Journal of Mathematics and Mathematical Sciences 3
Two new functions or pseudopotentials 1199103and 119910
4can be
introduced which are defined by the transformation
1199103=1199102
1199101
1199104=1199101
1199102
(16)
Then from (15) the following forms which have a Riccatistructure result
1205723= 1198891199103minus 1205963+ 211991031205961+ 1199102
31205962
1205724= 1198891199104minus 1205962minus 211991041205961+ 1199102
41205963
(17)
These equations could also be thought of as Riccati equationsfor 1199103and 119910
4
Theorem3 (i)Theone forms12057231205724given by (17) have exterior
derivatives
1198891205723= 211991031205991+ 1199102
31205992minus 1205993+ 21205723and (1205961+ 11991031205962)
1198891205724= minus 2119910
41205991minus 1205992+ 1199102
41205993+ 21205724and (minus120596
1+ 11991041205963)
(18)
Consequently results (18) are contained in the ring spanned by120599119894 and 120572
119895
(ii) Define the forms 1205901= 1205961+ 11991031205962and 120590
2= minus120596
1+
11991041205963appearing in (18) The exterior derivatives of 120590
1and 120590
2
are found to be
1198891205901= 1205991+ 11991031205992+ 1205723and 1205962
1198891205902= minus1205991+ 11991031205992+ 1205724and 1205962
(19)
Therefore 1198891205901equiv 0 and 119889120590
2equiv 0 mod 120599
119894 120572119895
The proof of this Theorem proceeds along exactly thesame lines as Theorem 1 The 119878119871(2R) structure and theconnection interpretation can be based on the forms 120572
3 1205724
At this point the process can be continued Two morepseudopotentials 119910
5and 119910
6can be introduced and the
differential system can be extended by including two moreone forms 120572
5and 120572
6 The specific structure of these forms is
suggested byTheorem 3
Theorem 4 Define two one forms 1205725and 120572
6as
1205725= 1198891199105minus 1205961minus 11991031205962 120572
6= 1198891199106+ 1205961minus 11991041205963 (20)
The exterior derivatives of the one forms (20) are given by theexpressions
1198891205725= minus1205991minus 11991031205993minus 1205723and 1205962 119889120572
6= 1205991minus 11991041205993minus 1205724and 1205963
(21)
Results (21) specify the closure properties of the forms 1205725and
1205726 This theorem is proved along similar lines keeping in mind
that the results for 1198891199103and 119889119910
4are obtained from (17)
A final extension can be made by adding two additionalpseudopotentials119910
7and1199108 At each stage the ideal of forms is
being enlarged and is found to be closed over the underlyingsubideal which does not contain the two new forms
Theorem 5 Define the one forms 1205727and 120572
8by means of
1205727= 1198891199107minus 119890minus211991051205962 120572
8= 1198891199108minus 119890minus211991061205963 (22)
The exterior derivatives of the forms 1205727and 120572
8are given by
1198891205727= 2119890minus211991051205725and 1205962minus 119890minus211991051205992
1198891205728= 2119890minus211991061205726and 1205963minus 119890minus211991061205993
(23)
and are closed over the prolonged ideal
3 119874(3) Prolongations
The first 3 times 3 problem we consider is formulated in terms ofa set of one forms 120596
119894for 119894 = 1 2 3 The following system of
Pfaffian equations is to be associated to a specific nonlinearequation
120572119894= 0 120572
119894= 119889119910119894minus Ω119894119895119910119895 119894 119895 = 1 2 3 (24)
In (24) Ω is a traceless 3 times 3 matrix of one forms Thenonlinear equation to emerge is expressed as the vanishingof a traceless 3 times 3matrix of two forms Θ
Θ = 0 Θ = 119889Ω minus Ω and Ω (25)These can be considered as integrability conditions for (24)The closure property the gauge transformation and the gaugetheoretic interpretation can also hold for 3 times 3 systemsExplicitly the matrixΩ is given by
Ω = (
0 minus1205961
1205962
1205961
0 minus1205963
minus1205962
1205963
0
) (26)
Using (26) in (24) and (25) the following prolonged differen-tial system is obtained
1198891199101= 1205721minus 11991021205961+ 11991031205962 119889120596
1= 1205991minus 1205962and 1205963
1198891199102= 1205722+ 11991011205961minus 11991031205963 119889120596
2= 1205992minus 1205963and 1205961
1198891199103= 1205723minus 11991011205962+ 11991021205963 119889120596
3= 1205993minus 1205961and 1205962
(27)
By straightforward exterior differentiation of each 120572119894and
using (27) the followingTheorem results
Theorem 6 The 120572119894given in (27) have exterior derivatives
which are contained in the ring spanned by 1205991198943
1and 120572
1198953
1and
given explicitly as1198891205721= 11991021205991minus 11991031205992minus 1205961and 1205722+ 1205962and 1205723
1198891205722= minus 119910
11205991+ 11991031205993+ 1205961and 1205721minus 1205963and 1205723
1198891205723= 11991011205992minus 11991021205993minus 1205962and 1205721+ 1205963and 1205722
(28)
The one forms 1205721198943
1admit a series of Riccati representa-
tions which can be realized by defining six new one forms
1199102
11205724= 11991011205722minus 11991021205721 119910
2
11205725= 11991011205723minus 11991031205721
1199102
21205726= 11991021205721minus 11991011205722
1199102
21205727= 11991021205723minus 11991031205722 119910
2
31205728= 11991031205721minus 11991011205723
1199102
31205729= 11991031205722minus 11991021205723
(29)
4 International Journal of Mathematics and Mathematical Sciences
In effect the larger 3times3 system is breaking up into several 2times2systems To write the new one forms explicitly introduce thenew functions 119910
1198959
4which are defined in terms of the original
1199101198943
1as follows
1199104=1199102
1199101
1199105=1199103
1199101
1199106=1199101
1199102
1199107=1199103
1199101
1199108=1199101
1199103
1199109=1199102
1199103
(30)
In terms of the functions defined in (30) the 1205721198959
4are given
as
1205724= 1198891199104minus (1 + 119910
2
4) 1205961+ 119910411991051205962+ 11991051205963
1205725= 1198891199105minus 119910411991051205961+ (1 + 119910
2
5) 1205962minus 11991041205963
1205726= 1198891199106+ (1 + 119910
2
6) 1205961minus 11991071205962minus 119910611991071205963
1205727= 1198891199107+ 119910611991071205961+ 11991061205962minus (1 + 119910
2
7) 1205963
1205728= 1198891199108+ 11991091205961minus (1 + 119910
2
8) 1205962+ 119910811991091205963
1205729= 1198891199109minus 11991081205961minus 119910811991091205962+ (1 + 119910
2
9) 1205963
(31)
To state the next theorem we need to define the followingthree matrices
Ω1= (
211991041205961minus 11991051205962
minus11991041205962minus 1205963
11991051205961+ 1205963
11991041205961minus 211991051205962
)
Ω2= (
minus211991061205961+ 11991071205963
1205962+ 11991061205963
minus11991071205961minus 1205966
minus11991061205961+ 211991071205963
)
Ω3= (
211991081205962minus 11991091205963
minus1205961minus 11991091205963
1205961+ 11991091205962
11991081205962minus 211991091205963
)
(32)
Theorem 7 The closure properties for the forms 1205721198949
4given in
(31) can be summarized in the form
119889(1205724
1205725
) = (minus (1 + 119910
2
4) 1205991+ 119910411991051205992+ 11991051205993
minus119910411991051205991+ (1 + 119910
2
5) 1205992minus 11991041205993
)
+ Ω1and (
1205724
1205725
)
119889 (1205726
1205727
) = ((1 + 119910
2
6) 1205991minus 11991071205992minus 119910611991071205993
119910611991071205991+ 11991061205992minus (1 + 119910
2
7) 1205993
)
+ Ω2and (
1205726
1205727
)
119889 (1205728
1205729
) = (11991011205991minus (1 + 119910
2
8) 1205992+ 119910811991091205993
minus11991081205991minus 119910811991091205992+ (1 + 119910
2
9) 1205993
)
+ Ω3and (
1205728
1205729
)
(33)
The exterior derivatives are therefore contained in the ringspanned by 120599
1198943
1and the 120572
1198959
4
In terms of Ω119894 a corresponding matrix of two forms Θ
119894
can be defined in terms of the corresponding Ω119894defined in
(32)
Θ119894= 119889Ω119894minus Ω119894and Ω119894 119894 = 1 2 3 (34)
Theorem 8 The 2 times 2matrix of two forms Θ119894defined by (34)
is contained in the ring of forms spanned by 1205991198943
1coupled with
either 1205724 1205725 1205726 1205727 or 120572
8 1205729when 119894 = 1 2 3 respectively
Proof DifferentiatingΩ1and simplifying we have
Θ1= 119889Ω1minus Ω1and Ω1
= (211991041205991minus 11991051205992+ 21205724and 1205961minus 1205725and 1205962
minus11991041205992minus 1205993minus 1205724and 1205962
11991051205991+ 1205993+ 1205725and 1205961
11991041205991minus 211991051205992+ 1205724and 1205961minus 21205725and 1205962
)
(35)
Similarmatrix expressions can be found for the cases inwhichΩ1is replaced by Ω
2orΩ3 respectively
Unlike Ω given in (26) the Ω119894in (32) are not traceless
Define their traces to be
120581119894= trΩ
119894 119894 = 1 2 3 (36)
These traces provide convenient ways of generating conser-vation laws on account of the followingTheorem
Theorem 9 The exterior derivatives of traces (36) are given by
1
31198891205811= 11991041205991minus 11991051205992minus 1205961and 1205724+ 1205962and 1205725
1
31198891205812= minus 119910
61205991+ 11991071205993+ 1205961and 1205726minus 1205963and 1205727
1
31198891205813= 11991081205992minus 11991091205993minus 1205962and 1205728+ 1205963and 1205729
(37)
Results (37) are contained in the ring spanned by 1205991198943
1and
1205721198959
4
International Journal of Mathematics and Mathematical Sciences 5
4 119878119880(3) Prolongations
To formulate a 3 times 3 119878119880(3) problem the set of Pfaffianequations
120572119894= 0 120572
119894= 119889119910119894minus Ω119894119895119910119895 119894 119895 = 1 2 3 (38)
are associated with the nonlinear equation In (38) Ω is atraceless 3 times 3 matrix consisting of a system of one formsThe nonlinear equation to be considered is expressed as thevanishing of a traceless 3times3matrix of two formsΘ exactly asin (25) which constitute the integrability condition for (38)
A 3times3matrix representation of the Lie algebra for 119878119880(3) isintroduced by means of generators 120582
119895for 119895 = 1 8 which
satisfy the following set of commutation relations
[120582119897 120582119898] = 2119894 119891
119897119898119899120582119899 (39)
The structure constants 119891119897119898119899
are totally antisymmetric in119897 119898 119899The one formΩ is expressed in terms of the generators120582119894as
Ω =
8
sum
119897=1
120596119897120582119897 (40)
Then the two forms Θ can be written as
Θ =
8
sum
119897=1
120599119897120582119897 120599119897= 119889120596119897minus 119894119891119897119898119899
120596119898and 120596119899 (41)
The nonlinear equation to be solved has the form 120599119897= 0 for
119897 = 1 8It will be useful to display (40) and (41) by using the
nonzero structure constants given in (39) since thesemay notbe readily accessible An explicit representation for thematrixΩ used here is given by
Ω = (
1205963+
1
radic3
1205968
1205961minus 1198941205962
1205964minus 1198941205965
1205961+ 1198941205962
minus1205963+
1
radic3
12059681205966minus 1198941205967
1205964+ 1198941205965
1205966+ 1198941205967
minus2
radic3
1205968
) (42)
Moreover in order that the presentation can be easier tofollow the eight forms 119889120596
119894specified by (41) will be given
explicitly
1198891205961= 1205991+ 21198941205962and 1205963+ 1198941205964and 1205967minus 1198941205965and 1205966
1198891205962= 1205992minus 21198941205961and 1205963+ 1198941205964and 1205966+ 1198941205965and 1205967
1198891205963= 1205993+ 21198941205961and 1205962+ 1198941205964and 1205965minus 1198941205966and 1205967
1198891205964= 1205994minus 1198941205961and 1205967minus 1198941205962and 1205966minus 1198941205963and 1205965+ radic3119894120596
5and 1205968
1198891205965= 1205995+ 1198941205961and 1205966minus 1198941205962and 1205967+ 1198941205963and 1205964minus radic3119894120596
4and 1205968
1198891205966= 1205996minus 1198941205961and 1205965+ 1198941205962and 1205964+ 1198941205963and 1205967+ radic3119894120596
7and 1205968
1198891205967= 1205997+ 1198941205961and 1205964+ 1198941205962and 1205965minus 1198941205963and 1205966minus radic3119894120596
6and 1205968
1198891205968= 1205998+ radic3119894120596
4and 1205965+ radic3119894120596
6and 1205967
(43)
Substituting (42) into (38) the following system of one forms1205721198943
1is obtained
1205721= 1198891199101minus (1205963+
1
radic3
1205968)1199101minus (1205961minus 1198941205962) 1199102minus (1205964minus 1198941205965) 1199103
1205722= 1198891199102minus (1205961+ 1198941205962) 1199101+ (1205963minus
1
radic3
1205968)1199102minus (1205966minus 1198941205967) 1199103
1205723= 1198891199103minus (1205964+ 1198941205965) 1199101minus (1205966+ 1198941205967) 1199102+
2
radic3
12059681199103
(44)
The increase in complexity of this system makes it oftennecessary to resort to the use of symbolic manipulation tocarry out longer calculations and for the most part onlyresults are given
Theorem10 Theexterior derivatives of the120572119894in (44) are given
by
1198891205721= minus 119910
2(1205991minus 1198941205992) minus 11991011205993minus 1199103(1205994minus 1198941205995)
minus1
radic3
11991011205998+ (1205963+
1
radic3
1205968) and 1205721
+ (1205961minus 1198941205962) and 1205722+ (1205964minus 1198941205965) and 1205723
1198891205722= minus 119910
1(1205991+ 1198941205992) + 11991021205993
minus1
radic3
11991021205998minus 1199103(1205996minus 1198941205997) + (120596
1+ 1198941205962) and 1205721
minus (1205963minus
1
radic3
1205968) and 1205722+ (1205966minus 1198941205967) and 1205723
1198891205723= minus 119910
1(1205994+ 1198941205995) minus 1199102(1205996+ 1198941205997)
+2
radic3
11991031205998+ (1205964+ 1198941205965) and 1205721
+ (1205966+ 1198941205967) and 1205722minus
2
radic3
1205968and 1205723
(45)
In order to keep the notation concise an abbreviation willbe introduced Suppose that 120574
119894 is a system of forms and 119894 119895
are integers then we make the abbreviation
120574119894119895plusmn
= 120574119894plusmn 119894120574119895 (46)
At this point quadratic pseudopotentials can be introducedin terms of the homogeneous variables of the same form as
6 International Journal of Mathematics and Mathematical Sciences
(30) In the same way that (31) was produced the followingPfaffian equations based on the set 120572
1198943
1in (44) are obtained
1205724= 1198891199104minus 12059612+
+ 211991041205963+ 1199102
412059612minus
minus 119910512059667minus
+ 1199104119910512059645minus
1205725= 1198891199105minus 12059645+
+ 1199105(1205963+ radic3120596
8)
+ 1199102
512059645minus
minus 119910412059667+
+ 1199104119910512059612minus
1205726= 1198891199106minus 12059612minus
minus 211991061205963+ 1199102
612059612+
minus 119910712059645minus
+ 1199106119910712059667minus
1205727= 1198891199107minus 12059667+
minus 1199107(1205963minus radic3120596
8)
+ 1199102
712059667minus
minus 119910612059645+
+ 1199106119910712059612+
1205728= 1198891199108minus 12059645minus
minus 1199108(1205963+ radic3120596
8)
+ 1199102
812059645+
minus 119910912059612minus
+ 1199108119910912059667+
1205729= 1198891199109minus 12059667minus
+ 1199109(1205963minus radic3120596
8)
+ 1199102
912059667+
minus 119910812059612+
+ 1199108119910912059645+
(47)
These are coupledRiccati equations for the pairs of pseudopo-tentials (119910
4 1199105) (1199106 1199107) and (119910
8 1199109) respectively
Define the following set of 2 times 2matrices of one formsΩ119894
for 119894 = 1 2 3 as
Ω1=(minus21205963minus2119910412059612minusminus119910512059645minus 12059667minusminus119910412059645minus
12059667+minus119910512059612minus minus1205963minusradic31205968minus119910412059612minusminus2119910512059645minus
)
Ω2=(21205963minus2119910612059612+ minus 119910712059667minus 12059645minusminus119910612059667minus
12059645+minus119910712059612+ 1205963minusradic31205968minus119910612059612+minus2119910712059667minus
)
Ω3=(1205963+radic31205968minus2119910812059645+minus119910912059667+ 12059612minusminus119910812059667+
12059612+minus119910912059645+ minus1205963+radic31205968minus119910812059645+minus2119910912059667+
)
(48)
Making use of the matrices Ω119894defined in (48) the following
result can be stated
Theorem 11 The closure properties of the set of forms 1205721198949
4
given by (47) can be expressed in terms of the Ω119894as follows
119889(12057241205725)
= ((1199102
4minus 1) 1205991minus119894 (119910
2
4+ 1) 1205992+211991041205993+1199104119910512059945minusminus119910512059967minus
1199104119910512059912minus+11991051205993+(1199102
4minus 1) 1205994minus119894 (119910
2
5+ 1) 1205995minus119910412059967++
radic311991051205998
)
+Ω1 and (12057241205725)
119889 (12057261205727)
= ((1199102
6minus 1) 1205991+119894 (119910
2
6+ 1) 1205992minus211991061205993minus119910712059945minus+1199106119910712059967minus
1199106119910712059912+minus11991071205993minus119910612059945++(1199102
7minus 1) 1205996minus119894 (119910
2
7+ 1) 1205997+
radic311991071205998
)
+Ω2 and (12057261205727)
119889 (12057281205729)
= (minus119910912059912minusminus11991081205993+(119910
2
8minus 1) 1205994+119894 (119910
2
8+ 1) 1205995+1199108119910912059967+minus
radic311991081205998
minus119910812059912++11991091205993+1199108119910912059945++(1199102
9minus 1) 1205996+119894 (119910
2
9+ 1) 1205997minus
radic311991091205998
)
+Ω3 and (12057281205729)
(49)
Based on the forms Ω119894given in (48) we can differentiate
to define the following matrices of two forms 120585119894given by
120585119894= 119889Ω119894minus Ω119894and Ω119894 (50)
Theorem 12 The forms 120585119894defined in (50) are given explicitly
by the matrices
1205851
=(
212059612+ and 1205724+12059645minus and 1205725 12059645minus and 1205724minus119910412059945minus+12059967minus
minus2119910412059912minus minus 21205993 minus 119910512059945minus12059612minus and 1205724+212059645minus and 1205725
12059612minus and 1205725minus119910512059912minus+12059967+ minus119910412059912minusminus1205993 minus 212059945minus minusradic31205998
)
1205852
=(
212059612+ and 1205726+12059667minus and 1205727 12059667minus and 1205726+12059945minus minus 119910612059967minus
minus2119910612059912+ + 1205993 minus 119910712059967minus12059612+ and 1205726+212059667minus and 1205727minus119910612059912+
12059612+ and 1205727 minus 1199107 12059912+ + 12059945+ +1205993 minus 2119910712059967minus minusradic31205998
)
1205853
=(
212059645+ and 1205728+12059667+ and 1205729+1205993 12059667+ and 1205728+12059912minusminus119910812059967+
minus2119910812059945+ minus 119910912059967+ +radic3120599812059645+ and 1205728+212059667+ and 1205729minus1205993
12059645+ and 1205729+12059912+minus119910912059945+ minus119910812059945+ minus 2119910912059967+ +radic31205998
)
(51)
From these results it is concluded that 1205851is contained in
the ring of 1205724 1205725 and the 120599
119897 1205852is contained in the ring of
1205726 1205727 and 120599
119897 and 120585
3is in the ring of 120572
8 1205729 and 120599
119897
The two forms 1205851198943
1therefore vanish for the solutions of the
nonlinear equations (39) and of the coupled Riccati equations120572119895= 09
4 As in the case of 119874(3) the one forms Ω
119894are not
traceless Denoting the trace of Ω119894by
120591119894= trΩ
119894 (52)
the following theorem then follows
Theorem 13 The closure properties of the exterior derivativesof the traces 120591
119894are given by
1
31198891205911= 12059612minus
and 1205724+ 12059645minus
and 1205725
minus 119910412059912minus
minus 1205993minus 119910512059945minus
minus1
radic3
1205998
International Journal of Mathematics and Mathematical Sciences 7
1
31198891205912= 12059612+
and 1205726+ 12059667minus
and 1205727
minus 119910612059912+
+ 1205993minus 119910712059967minus
minus1
radic3
1205998
1
31198891205913= 12059645+
and 1205728+ 12059667+
and 1205729
minus 119910812059945+
minus 119910912059967+
+2
radic3
1205998
(53)
The one forms (52) then can be used to generate con-servation laws Note that as in the 119874(3) case a 3 times 3
problemΩ has been reduced to three separate 2times2 problemsin terms of the matrices Ω
119897 Further prolongation can be
continued beginning with the one formsΩ119897given in (48) To
briefly outline the further steps in the procedure a system ofPfaffians
119897119895 is introduced which are based on the one forms
Ω119897
119897119895= 0
119897119895= 119889119910119897119895minus (Ω119897)119895119896119910119897119896 (54)
The subscript 119897 in 119910119897119895and
119897119895indicates that they belong to the
subsystem defined byΩ119897 and it is not summed over Exterior
differentiation of 119897119895yields
119889119897119895= (Ω119897)119895119896and 119897119896minus (Θ)
119895119896119910119897119896 (55)
The 119910119897119895 are pseudopotentials for the original nonlinear
equation (39) Next quadratic pseudopotentials are includedas the homogeneous variables and the prolongation can becontinued
5 A Conservation Law and Summary
These types of results turn out to be very useful for furtherstudy of integrable equationsThey can be used for generatinginfinite numbers of conservation laws In addition the resultsare independent of any further structure of the forms 120596
119894in
all cases In fact the one form Ω need not be thought of asuniqueThis is due to the fact thatΩ andΘ are form invariantunder the gauge transformationΩ rarr 120596
1015840= 119889119860 119860
minus1+119860Ω119860
minus1
and Θ rarr Θ1015840= 119860Θ119860
minus1 where in the 119878119871(2R) case 119860 is anarbitrary 2 times 2 space-time-dependent matrix of determinantone The gauge transformation property holds in the 3 times 3
case as well The pseudopotentials serve as potentials forconservation laws in a generalized senseThey can be definedunder a choice of Pfaffian forms such as
120572119894= 0 120572
119894= 119889119910119894+ 119865119894119889119909 + 119866
119894119889119905 (56)
with the property that the exterior derivatives 119889120572119894are con-
tained in the ring spanned by 120572119894 and 120599
119897
119889120572119894= sum
119895
119860119894119895and 120572119895+sum
119897
Γ119894119897120599119897 (57)
This can be thought of as a generalization of the FrobeniusTheorem for complete integrability of Pfaffian systems
Theorem 3 implies that 119889120590119894= 0when 119894 = 1 2 for solutions
of the original equation If either of these forms is expressedas 120590 = I119889119909 +J119889119905 then 119889120590 = 0 implies that
120597I
120597119905minus120597J
120597119905= 0 (58)
ThusI is a conserved density andJ a conserved current Letus finally represent 120596
1= 1198861119889119909 + 119887
1119889119905 1205962= 1198862119889119909 + 119887
2119889119905 and
1205963= 120578119889119909 + 119887
3119889119905 where 120578 is a parameter The 119909-dependent
piece of 1205723in (17) implies
1199103119909
+ 211988611199103+ 11988621199102
3minus 120578 = 0 (59)
By substituting an asymptotic expansion around 120578 = infin for1199103in (59) of the form
1199103=
infin
sum
0
120578minus119899119884119899 (60)
a recursion for the 119884119899is obtained Thus (59) becomes
sum
119899
120578minus119899119884119899119909
+ 21198861sum
119899
120578minus119899119884119899
+ 1198862(sum
119899
120578minus119899119884119899)
2
minus 120578 = 0
(61)
Expanding the power collecting coefficients of 120578 and equat-ing coefficients of 120578 to zero we get
1198841119909
+ 211988611198841= 1 119884
119899119909+ 21198861119884119899+ 1198862
119899minus1
sum
119896=1
119884119899minus119896
119884119896= 0
(62)
The consistency of solving 1205723by using just the 119909 part is
guaranteed by complete integrability The 119909 part of the form1205901is expressed as
(1205901)119909= (1198861+
infin
sum
119899=1
120578minus1198991198841198991198862)119889119909 (63)
Consequently from (58) the 119899th conserved density is
I119899= 1198862119884119899 (64)
The existence of links between the types of prolongationhere and other types of prolongations which are based onclosed differential systems is a subject for further work
References
[1] F B Estabrook and H D Wahlquist ldquoClassical geometriesdefined by exterior differential systems on higher frame bun-dlesrdquo Classical and Quantum Gravity vol 6 no 3 pp 263ndash2741989
[2] H Cartan Differential Forms Dover Mineola NY USA 2006[3] M J Ablowitz D J Kaup A C Newell and H Segur ldquoMethod
for solving the sine-Gordon equationrdquo Physical Review Lettersvol 30 pp 1262ndash1264 1973
8 International Journal of Mathematics and Mathematical Sciences
[4] M J Ablowitz D K Kaup A C Newell and H SegurldquoNonlinear-evolution equations of physical significancerdquo Phys-ical Review Letters vol 31 pp 125ndash127 1973
[5] R Sasaki ldquoPseudopotentials for the general AKNS systemrdquoPhysics Letters A vol 73 no 2 pp 77ndash80 1979
[6] R Sasaki ldquoGeometric approach to soliton equationsrdquo Proceed-ings of the Royal Society London vol 373 no 1754 pp 373ndash3841980
[7] M Crampin ldquoSolitons and 119878119871(2R)rdquo Physics Letters A vol 66no 3 pp 170ndash172 1978
[8] D J Kaup and J Yang ldquoThe inverse scattering transform andsquared eigenfunctions for a degenerate 3 times 3 operatorrdquo InverseProblems vol 25 no 10 Article ID 105010 2009
[9] D J Kaup and R A Van Gorder ldquoThe inverse scatteringtransform and squared eigenfunctions for the nondegenerate3 times 3 operator and its soliton structurerdquo Inverse Problems vol26 no 5 Article ID 055005 2010
[10] P Bracken ldquoIntrinsic formulation of geometric integrabilityand associated Riccati system generating conservation lawsrdquoInternational Journal of Geometric Methods in Modern Physicsvol 6 no 5 pp 825ndash837 2009
[11] D J Kaup and R A Van Gorder ldquoSquared eigenfunctions andthe perturbation theory for the nondegenerate N timesN operatora general outlinerdquo Journal of Physics A vol 43 Article ID434019 2010
[12] H D Wahlquist and F B Estabrook ldquoProlongation structuresof nonlinear evolution equationsrdquo Journal of MathematicalPhysics vol 16 pp 1ndash7 1975
[13] P Bracken ldquoOn two-dimensional manifolds with constantGaussian curvature and their associated equationsrdquo Interna-tional Journal of Geometric Methods in Modern Physics vol 9no 3 Article ID 1250018 2012
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Stochastic AnalysisInternational Journal of
4 International Journal of Mathematics and Mathematical Sciences
In effect the larger 3times3 system is breaking up into several 2times2systems To write the new one forms explicitly introduce thenew functions 119910
1198959
4which are defined in terms of the original
1199101198943
1as follows
1199104=1199102
1199101
1199105=1199103
1199101
1199106=1199101
1199102
1199107=1199103
1199101
1199108=1199101
1199103
1199109=1199102
1199103
(30)
In terms of the functions defined in (30) the 1205721198959
4are given
as
1205724= 1198891199104minus (1 + 119910
2
4) 1205961+ 119910411991051205962+ 11991051205963
1205725= 1198891199105minus 119910411991051205961+ (1 + 119910
2
5) 1205962minus 11991041205963
1205726= 1198891199106+ (1 + 119910
2
6) 1205961minus 11991071205962minus 119910611991071205963
1205727= 1198891199107+ 119910611991071205961+ 11991061205962minus (1 + 119910
2
7) 1205963
1205728= 1198891199108+ 11991091205961minus (1 + 119910
2
8) 1205962+ 119910811991091205963
1205729= 1198891199109minus 11991081205961minus 119910811991091205962+ (1 + 119910
2
9) 1205963
(31)
To state the next theorem we need to define the followingthree matrices
Ω1= (
211991041205961minus 11991051205962
minus11991041205962minus 1205963
11991051205961+ 1205963
11991041205961minus 211991051205962
)
Ω2= (
minus211991061205961+ 11991071205963
1205962+ 11991061205963
minus11991071205961minus 1205966
minus11991061205961+ 211991071205963
)
Ω3= (
211991081205962minus 11991091205963
minus1205961minus 11991091205963
1205961+ 11991091205962
11991081205962minus 211991091205963
)
(32)
Theorem 7 The closure properties for the forms 1205721198949
4given in
(31) can be summarized in the form
119889(1205724
1205725
) = (minus (1 + 119910
2
4) 1205991+ 119910411991051205992+ 11991051205993
minus119910411991051205991+ (1 + 119910
2
5) 1205992minus 11991041205993
)
+ Ω1and (
1205724
1205725
)
119889 (1205726
1205727
) = ((1 + 119910
2
6) 1205991minus 11991071205992minus 119910611991071205993
119910611991071205991+ 11991061205992minus (1 + 119910
2
7) 1205993
)
+ Ω2and (
1205726
1205727
)
119889 (1205728
1205729
) = (11991011205991minus (1 + 119910
2
8) 1205992+ 119910811991091205993
minus11991081205991minus 119910811991091205992+ (1 + 119910
2
9) 1205993
)
+ Ω3and (
1205728
1205729
)
(33)
The exterior derivatives are therefore contained in the ringspanned by 120599
1198943
1and the 120572
1198959
4
In terms of Ω119894 a corresponding matrix of two forms Θ
119894
can be defined in terms of the corresponding Ω119894defined in
(32)
Θ119894= 119889Ω119894minus Ω119894and Ω119894 119894 = 1 2 3 (34)
Theorem 8 The 2 times 2matrix of two forms Θ119894defined by (34)
is contained in the ring of forms spanned by 1205991198943
1coupled with
either 1205724 1205725 1205726 1205727 or 120572
8 1205729when 119894 = 1 2 3 respectively
Proof DifferentiatingΩ1and simplifying we have
Θ1= 119889Ω1minus Ω1and Ω1
= (211991041205991minus 11991051205992+ 21205724and 1205961minus 1205725and 1205962
minus11991041205992minus 1205993minus 1205724and 1205962
11991051205991+ 1205993+ 1205725and 1205961
11991041205991minus 211991051205992+ 1205724and 1205961minus 21205725and 1205962
)
(35)
Similarmatrix expressions can be found for the cases inwhichΩ1is replaced by Ω
2orΩ3 respectively
Unlike Ω given in (26) the Ω119894in (32) are not traceless
Define their traces to be
120581119894= trΩ
119894 119894 = 1 2 3 (36)
These traces provide convenient ways of generating conser-vation laws on account of the followingTheorem
Theorem 9 The exterior derivatives of traces (36) are given by
1
31198891205811= 11991041205991minus 11991051205992minus 1205961and 1205724+ 1205962and 1205725
1
31198891205812= minus 119910
61205991+ 11991071205993+ 1205961and 1205726minus 1205963and 1205727
1
31198891205813= 11991081205992minus 11991091205993minus 1205962and 1205728+ 1205963and 1205729
(37)
Results (37) are contained in the ring spanned by 1205991198943
1and
1205721198959
4
International Journal of Mathematics and Mathematical Sciences 5
4 119878119880(3) Prolongations
To formulate a 3 times 3 119878119880(3) problem the set of Pfaffianequations
120572119894= 0 120572
119894= 119889119910119894minus Ω119894119895119910119895 119894 119895 = 1 2 3 (38)
are associated with the nonlinear equation In (38) Ω is atraceless 3 times 3 matrix consisting of a system of one formsThe nonlinear equation to be considered is expressed as thevanishing of a traceless 3times3matrix of two formsΘ exactly asin (25) which constitute the integrability condition for (38)
A 3times3matrix representation of the Lie algebra for 119878119880(3) isintroduced by means of generators 120582
119895for 119895 = 1 8 which
satisfy the following set of commutation relations
[120582119897 120582119898] = 2119894 119891
119897119898119899120582119899 (39)
The structure constants 119891119897119898119899
are totally antisymmetric in119897 119898 119899The one formΩ is expressed in terms of the generators120582119894as
Ω =
8
sum
119897=1
120596119897120582119897 (40)
Then the two forms Θ can be written as
Θ =
8
sum
119897=1
120599119897120582119897 120599119897= 119889120596119897minus 119894119891119897119898119899
120596119898and 120596119899 (41)
The nonlinear equation to be solved has the form 120599119897= 0 for
119897 = 1 8It will be useful to display (40) and (41) by using the
nonzero structure constants given in (39) since thesemay notbe readily accessible An explicit representation for thematrixΩ used here is given by
Ω = (
1205963+
1
radic3
1205968
1205961minus 1198941205962
1205964minus 1198941205965
1205961+ 1198941205962
minus1205963+
1
radic3
12059681205966minus 1198941205967
1205964+ 1198941205965
1205966+ 1198941205967
minus2
radic3
1205968
) (42)
Moreover in order that the presentation can be easier tofollow the eight forms 119889120596
119894specified by (41) will be given
explicitly
1198891205961= 1205991+ 21198941205962and 1205963+ 1198941205964and 1205967minus 1198941205965and 1205966
1198891205962= 1205992minus 21198941205961and 1205963+ 1198941205964and 1205966+ 1198941205965and 1205967
1198891205963= 1205993+ 21198941205961and 1205962+ 1198941205964and 1205965minus 1198941205966and 1205967
1198891205964= 1205994minus 1198941205961and 1205967minus 1198941205962and 1205966minus 1198941205963and 1205965+ radic3119894120596
5and 1205968
1198891205965= 1205995+ 1198941205961and 1205966minus 1198941205962and 1205967+ 1198941205963and 1205964minus radic3119894120596
4and 1205968
1198891205966= 1205996minus 1198941205961and 1205965+ 1198941205962and 1205964+ 1198941205963and 1205967+ radic3119894120596
7and 1205968
1198891205967= 1205997+ 1198941205961and 1205964+ 1198941205962and 1205965minus 1198941205963and 1205966minus radic3119894120596
6and 1205968
1198891205968= 1205998+ radic3119894120596
4and 1205965+ radic3119894120596
6and 1205967
(43)
Substituting (42) into (38) the following system of one forms1205721198943
1is obtained
1205721= 1198891199101minus (1205963+
1
radic3
1205968)1199101minus (1205961minus 1198941205962) 1199102minus (1205964minus 1198941205965) 1199103
1205722= 1198891199102minus (1205961+ 1198941205962) 1199101+ (1205963minus
1
radic3
1205968)1199102minus (1205966minus 1198941205967) 1199103
1205723= 1198891199103minus (1205964+ 1198941205965) 1199101minus (1205966+ 1198941205967) 1199102+
2
radic3
12059681199103
(44)
The increase in complexity of this system makes it oftennecessary to resort to the use of symbolic manipulation tocarry out longer calculations and for the most part onlyresults are given
Theorem10 Theexterior derivatives of the120572119894in (44) are given
by
1198891205721= minus 119910
2(1205991minus 1198941205992) minus 11991011205993minus 1199103(1205994minus 1198941205995)
minus1
radic3
11991011205998+ (1205963+
1
radic3
1205968) and 1205721
+ (1205961minus 1198941205962) and 1205722+ (1205964minus 1198941205965) and 1205723
1198891205722= minus 119910
1(1205991+ 1198941205992) + 11991021205993
minus1
radic3
11991021205998minus 1199103(1205996minus 1198941205997) + (120596
1+ 1198941205962) and 1205721
minus (1205963minus
1
radic3
1205968) and 1205722+ (1205966minus 1198941205967) and 1205723
1198891205723= minus 119910
1(1205994+ 1198941205995) minus 1199102(1205996+ 1198941205997)
+2
radic3
11991031205998+ (1205964+ 1198941205965) and 1205721
+ (1205966+ 1198941205967) and 1205722minus
2
radic3
1205968and 1205723
(45)
In order to keep the notation concise an abbreviation willbe introduced Suppose that 120574
119894 is a system of forms and 119894 119895
are integers then we make the abbreviation
120574119894119895plusmn
= 120574119894plusmn 119894120574119895 (46)
At this point quadratic pseudopotentials can be introducedin terms of the homogeneous variables of the same form as
6 International Journal of Mathematics and Mathematical Sciences
(30) In the same way that (31) was produced the followingPfaffian equations based on the set 120572
1198943
1in (44) are obtained
1205724= 1198891199104minus 12059612+
+ 211991041205963+ 1199102
412059612minus
minus 119910512059667minus
+ 1199104119910512059645minus
1205725= 1198891199105minus 12059645+
+ 1199105(1205963+ radic3120596
8)
+ 1199102
512059645minus
minus 119910412059667+
+ 1199104119910512059612minus
1205726= 1198891199106minus 12059612minus
minus 211991061205963+ 1199102
612059612+
minus 119910712059645minus
+ 1199106119910712059667minus
1205727= 1198891199107minus 12059667+
minus 1199107(1205963minus radic3120596
8)
+ 1199102
712059667minus
minus 119910612059645+
+ 1199106119910712059612+
1205728= 1198891199108minus 12059645minus
minus 1199108(1205963+ radic3120596
8)
+ 1199102
812059645+
minus 119910912059612minus
+ 1199108119910912059667+
1205729= 1198891199109minus 12059667minus
+ 1199109(1205963minus radic3120596
8)
+ 1199102
912059667+
minus 119910812059612+
+ 1199108119910912059645+
(47)
These are coupledRiccati equations for the pairs of pseudopo-tentials (119910
4 1199105) (1199106 1199107) and (119910
8 1199109) respectively
Define the following set of 2 times 2matrices of one formsΩ119894
for 119894 = 1 2 3 as
Ω1=(minus21205963minus2119910412059612minusminus119910512059645minus 12059667minusminus119910412059645minus
12059667+minus119910512059612minus minus1205963minusradic31205968minus119910412059612minusminus2119910512059645minus
)
Ω2=(21205963minus2119910612059612+ minus 119910712059667minus 12059645minusminus119910612059667minus
12059645+minus119910712059612+ 1205963minusradic31205968minus119910612059612+minus2119910712059667minus
)
Ω3=(1205963+radic31205968minus2119910812059645+minus119910912059667+ 12059612minusminus119910812059667+
12059612+minus119910912059645+ minus1205963+radic31205968minus119910812059645+minus2119910912059667+
)
(48)
Making use of the matrices Ω119894defined in (48) the following
result can be stated
Theorem 11 The closure properties of the set of forms 1205721198949
4
given by (47) can be expressed in terms of the Ω119894as follows
119889(12057241205725)
= ((1199102
4minus 1) 1205991minus119894 (119910
2
4+ 1) 1205992+211991041205993+1199104119910512059945minusminus119910512059967minus
1199104119910512059912minus+11991051205993+(1199102
4minus 1) 1205994minus119894 (119910
2
5+ 1) 1205995minus119910412059967++
radic311991051205998
)
+Ω1 and (12057241205725)
119889 (12057261205727)
= ((1199102
6minus 1) 1205991+119894 (119910
2
6+ 1) 1205992minus211991061205993minus119910712059945minus+1199106119910712059967minus
1199106119910712059912+minus11991071205993minus119910612059945++(1199102
7minus 1) 1205996minus119894 (119910
2
7+ 1) 1205997+
radic311991071205998
)
+Ω2 and (12057261205727)
119889 (12057281205729)
= (minus119910912059912minusminus11991081205993+(119910
2
8minus 1) 1205994+119894 (119910
2
8+ 1) 1205995+1199108119910912059967+minus
radic311991081205998
minus119910812059912++11991091205993+1199108119910912059945++(1199102
9minus 1) 1205996+119894 (119910
2
9+ 1) 1205997minus
radic311991091205998
)
+Ω3 and (12057281205729)
(49)
Based on the forms Ω119894given in (48) we can differentiate
to define the following matrices of two forms 120585119894given by
120585119894= 119889Ω119894minus Ω119894and Ω119894 (50)
Theorem 12 The forms 120585119894defined in (50) are given explicitly
by the matrices
1205851
=(
212059612+ and 1205724+12059645minus and 1205725 12059645minus and 1205724minus119910412059945minus+12059967minus
minus2119910412059912minus minus 21205993 minus 119910512059945minus12059612minus and 1205724+212059645minus and 1205725
12059612minus and 1205725minus119910512059912minus+12059967+ minus119910412059912minusminus1205993 minus 212059945minus minusradic31205998
)
1205852
=(
212059612+ and 1205726+12059667minus and 1205727 12059667minus and 1205726+12059945minus minus 119910612059967minus
minus2119910612059912+ + 1205993 minus 119910712059967minus12059612+ and 1205726+212059667minus and 1205727minus119910612059912+
12059612+ and 1205727 minus 1199107 12059912+ + 12059945+ +1205993 minus 2119910712059967minus minusradic31205998
)
1205853
=(
212059645+ and 1205728+12059667+ and 1205729+1205993 12059667+ and 1205728+12059912minusminus119910812059967+
minus2119910812059945+ minus 119910912059967+ +radic3120599812059645+ and 1205728+212059667+ and 1205729minus1205993
12059645+ and 1205729+12059912+minus119910912059945+ minus119910812059945+ minus 2119910912059967+ +radic31205998
)
(51)
From these results it is concluded that 1205851is contained in
the ring of 1205724 1205725 and the 120599
119897 1205852is contained in the ring of
1205726 1205727 and 120599
119897 and 120585
3is in the ring of 120572
8 1205729 and 120599
119897
The two forms 1205851198943
1therefore vanish for the solutions of the
nonlinear equations (39) and of the coupled Riccati equations120572119895= 09
4 As in the case of 119874(3) the one forms Ω
119894are not
traceless Denoting the trace of Ω119894by
120591119894= trΩ
119894 (52)
the following theorem then follows
Theorem 13 The closure properties of the exterior derivativesof the traces 120591
119894are given by
1
31198891205911= 12059612minus
and 1205724+ 12059645minus
and 1205725
minus 119910412059912minus
minus 1205993minus 119910512059945minus
minus1
radic3
1205998
International Journal of Mathematics and Mathematical Sciences 7
1
31198891205912= 12059612+
and 1205726+ 12059667minus
and 1205727
minus 119910612059912+
+ 1205993minus 119910712059967minus
minus1
radic3
1205998
1
31198891205913= 12059645+
and 1205728+ 12059667+
and 1205729
minus 119910812059945+
minus 119910912059967+
+2
radic3
1205998
(53)
The one forms (52) then can be used to generate con-servation laws Note that as in the 119874(3) case a 3 times 3
problemΩ has been reduced to three separate 2times2 problemsin terms of the matrices Ω
119897 Further prolongation can be
continued beginning with the one formsΩ119897given in (48) To
briefly outline the further steps in the procedure a system ofPfaffians
119897119895 is introduced which are based on the one forms
Ω119897
119897119895= 0
119897119895= 119889119910119897119895minus (Ω119897)119895119896119910119897119896 (54)
The subscript 119897 in 119910119897119895and
119897119895indicates that they belong to the
subsystem defined byΩ119897 and it is not summed over Exterior
differentiation of 119897119895yields
119889119897119895= (Ω119897)119895119896and 119897119896minus (Θ)
119895119896119910119897119896 (55)
The 119910119897119895 are pseudopotentials for the original nonlinear
equation (39) Next quadratic pseudopotentials are includedas the homogeneous variables and the prolongation can becontinued
5 A Conservation Law and Summary
These types of results turn out to be very useful for furtherstudy of integrable equationsThey can be used for generatinginfinite numbers of conservation laws In addition the resultsare independent of any further structure of the forms 120596
119894in
all cases In fact the one form Ω need not be thought of asuniqueThis is due to the fact thatΩ andΘ are form invariantunder the gauge transformationΩ rarr 120596
1015840= 119889119860 119860
minus1+119860Ω119860
minus1
and Θ rarr Θ1015840= 119860Θ119860
minus1 where in the 119878119871(2R) case 119860 is anarbitrary 2 times 2 space-time-dependent matrix of determinantone The gauge transformation property holds in the 3 times 3
case as well The pseudopotentials serve as potentials forconservation laws in a generalized senseThey can be definedunder a choice of Pfaffian forms such as
120572119894= 0 120572
119894= 119889119910119894+ 119865119894119889119909 + 119866
119894119889119905 (56)
with the property that the exterior derivatives 119889120572119894are con-
tained in the ring spanned by 120572119894 and 120599
119897
119889120572119894= sum
119895
119860119894119895and 120572119895+sum
119897
Γ119894119897120599119897 (57)
This can be thought of as a generalization of the FrobeniusTheorem for complete integrability of Pfaffian systems
Theorem 3 implies that 119889120590119894= 0when 119894 = 1 2 for solutions
of the original equation If either of these forms is expressedas 120590 = I119889119909 +J119889119905 then 119889120590 = 0 implies that
120597I
120597119905minus120597J
120597119905= 0 (58)
ThusI is a conserved density andJ a conserved current Letus finally represent 120596
1= 1198861119889119909 + 119887
1119889119905 1205962= 1198862119889119909 + 119887
2119889119905 and
1205963= 120578119889119909 + 119887
3119889119905 where 120578 is a parameter The 119909-dependent
piece of 1205723in (17) implies
1199103119909
+ 211988611199103+ 11988621199102
3minus 120578 = 0 (59)
By substituting an asymptotic expansion around 120578 = infin for1199103in (59) of the form
1199103=
infin
sum
0
120578minus119899119884119899 (60)
a recursion for the 119884119899is obtained Thus (59) becomes
sum
119899
120578minus119899119884119899119909
+ 21198861sum
119899
120578minus119899119884119899
+ 1198862(sum
119899
120578minus119899119884119899)
2
minus 120578 = 0
(61)
Expanding the power collecting coefficients of 120578 and equat-ing coefficients of 120578 to zero we get
1198841119909
+ 211988611198841= 1 119884
119899119909+ 21198861119884119899+ 1198862
119899minus1
sum
119896=1
119884119899minus119896
119884119896= 0
(62)
The consistency of solving 1205723by using just the 119909 part is
guaranteed by complete integrability The 119909 part of the form1205901is expressed as
(1205901)119909= (1198861+
infin
sum
119899=1
120578minus1198991198841198991198862)119889119909 (63)
Consequently from (58) the 119899th conserved density is
I119899= 1198862119884119899 (64)
The existence of links between the types of prolongationhere and other types of prolongations which are based onclosed differential systems is a subject for further work
References
[1] F B Estabrook and H D Wahlquist ldquoClassical geometriesdefined by exterior differential systems on higher frame bun-dlesrdquo Classical and Quantum Gravity vol 6 no 3 pp 263ndash2741989
[2] H Cartan Differential Forms Dover Mineola NY USA 2006[3] M J Ablowitz D J Kaup A C Newell and H Segur ldquoMethod
for solving the sine-Gordon equationrdquo Physical Review Lettersvol 30 pp 1262ndash1264 1973
8 International Journal of Mathematics and Mathematical Sciences
[4] M J Ablowitz D K Kaup A C Newell and H SegurldquoNonlinear-evolution equations of physical significancerdquo Phys-ical Review Letters vol 31 pp 125ndash127 1973
[5] R Sasaki ldquoPseudopotentials for the general AKNS systemrdquoPhysics Letters A vol 73 no 2 pp 77ndash80 1979
[6] R Sasaki ldquoGeometric approach to soliton equationsrdquo Proceed-ings of the Royal Society London vol 373 no 1754 pp 373ndash3841980
[7] M Crampin ldquoSolitons and 119878119871(2R)rdquo Physics Letters A vol 66no 3 pp 170ndash172 1978
[8] D J Kaup and J Yang ldquoThe inverse scattering transform andsquared eigenfunctions for a degenerate 3 times 3 operatorrdquo InverseProblems vol 25 no 10 Article ID 105010 2009
[9] D J Kaup and R A Van Gorder ldquoThe inverse scatteringtransform and squared eigenfunctions for the nondegenerate3 times 3 operator and its soliton structurerdquo Inverse Problems vol26 no 5 Article ID 055005 2010
[10] P Bracken ldquoIntrinsic formulation of geometric integrabilityand associated Riccati system generating conservation lawsrdquoInternational Journal of Geometric Methods in Modern Physicsvol 6 no 5 pp 825ndash837 2009
[11] D J Kaup and R A Van Gorder ldquoSquared eigenfunctions andthe perturbation theory for the nondegenerate N timesN operatora general outlinerdquo Journal of Physics A vol 43 Article ID434019 2010
[12] H D Wahlquist and F B Estabrook ldquoProlongation structuresof nonlinear evolution equationsrdquo Journal of MathematicalPhysics vol 16 pp 1ndash7 1975
[13] P Bracken ldquoOn two-dimensional manifolds with constantGaussian curvature and their associated equationsrdquo Interna-tional Journal of Geometric Methods in Modern Physics vol 9no 3 Article ID 1250018 2012
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
International Journal of Mathematics and Mathematical Sciences 5
4 119878119880(3) Prolongations
To formulate a 3 times 3 119878119880(3) problem the set of Pfaffianequations
120572119894= 0 120572
119894= 119889119910119894minus Ω119894119895119910119895 119894 119895 = 1 2 3 (38)
are associated with the nonlinear equation In (38) Ω is atraceless 3 times 3 matrix consisting of a system of one formsThe nonlinear equation to be considered is expressed as thevanishing of a traceless 3times3matrix of two formsΘ exactly asin (25) which constitute the integrability condition for (38)
A 3times3matrix representation of the Lie algebra for 119878119880(3) isintroduced by means of generators 120582
119895for 119895 = 1 8 which
satisfy the following set of commutation relations
[120582119897 120582119898] = 2119894 119891
119897119898119899120582119899 (39)
The structure constants 119891119897119898119899
are totally antisymmetric in119897 119898 119899The one formΩ is expressed in terms of the generators120582119894as
Ω =
8
sum
119897=1
120596119897120582119897 (40)
Then the two forms Θ can be written as
Θ =
8
sum
119897=1
120599119897120582119897 120599119897= 119889120596119897minus 119894119891119897119898119899
120596119898and 120596119899 (41)
The nonlinear equation to be solved has the form 120599119897= 0 for
119897 = 1 8It will be useful to display (40) and (41) by using the
nonzero structure constants given in (39) since thesemay notbe readily accessible An explicit representation for thematrixΩ used here is given by
Ω = (
1205963+
1
radic3
1205968
1205961minus 1198941205962
1205964minus 1198941205965
1205961+ 1198941205962
minus1205963+
1
radic3
12059681205966minus 1198941205967
1205964+ 1198941205965
1205966+ 1198941205967
minus2
radic3
1205968
) (42)
Moreover in order that the presentation can be easier tofollow the eight forms 119889120596
119894specified by (41) will be given
explicitly
1198891205961= 1205991+ 21198941205962and 1205963+ 1198941205964and 1205967minus 1198941205965and 1205966
1198891205962= 1205992minus 21198941205961and 1205963+ 1198941205964and 1205966+ 1198941205965and 1205967
1198891205963= 1205993+ 21198941205961and 1205962+ 1198941205964and 1205965minus 1198941205966and 1205967
1198891205964= 1205994minus 1198941205961and 1205967minus 1198941205962and 1205966minus 1198941205963and 1205965+ radic3119894120596
5and 1205968
1198891205965= 1205995+ 1198941205961and 1205966minus 1198941205962and 1205967+ 1198941205963and 1205964minus radic3119894120596
4and 1205968
1198891205966= 1205996minus 1198941205961and 1205965+ 1198941205962and 1205964+ 1198941205963and 1205967+ radic3119894120596
7and 1205968
1198891205967= 1205997+ 1198941205961and 1205964+ 1198941205962and 1205965minus 1198941205963and 1205966minus radic3119894120596
6and 1205968
1198891205968= 1205998+ radic3119894120596
4and 1205965+ radic3119894120596
6and 1205967
(43)
Substituting (42) into (38) the following system of one forms1205721198943
1is obtained
1205721= 1198891199101minus (1205963+
1
radic3
1205968)1199101minus (1205961minus 1198941205962) 1199102minus (1205964minus 1198941205965) 1199103
1205722= 1198891199102minus (1205961+ 1198941205962) 1199101+ (1205963minus
1
radic3
1205968)1199102minus (1205966minus 1198941205967) 1199103
1205723= 1198891199103minus (1205964+ 1198941205965) 1199101minus (1205966+ 1198941205967) 1199102+
2
radic3
12059681199103
(44)
The increase in complexity of this system makes it oftennecessary to resort to the use of symbolic manipulation tocarry out longer calculations and for the most part onlyresults are given
Theorem10 Theexterior derivatives of the120572119894in (44) are given
by
1198891205721= minus 119910
2(1205991minus 1198941205992) minus 11991011205993minus 1199103(1205994minus 1198941205995)
minus1
radic3
11991011205998+ (1205963+
1
radic3
1205968) and 1205721
+ (1205961minus 1198941205962) and 1205722+ (1205964minus 1198941205965) and 1205723
1198891205722= minus 119910
1(1205991+ 1198941205992) + 11991021205993
minus1
radic3
11991021205998minus 1199103(1205996minus 1198941205997) + (120596
1+ 1198941205962) and 1205721
minus (1205963minus
1
radic3
1205968) and 1205722+ (1205966minus 1198941205967) and 1205723
1198891205723= minus 119910
1(1205994+ 1198941205995) minus 1199102(1205996+ 1198941205997)
+2
radic3
11991031205998+ (1205964+ 1198941205965) and 1205721
+ (1205966+ 1198941205967) and 1205722minus
2
radic3
1205968and 1205723
(45)
In order to keep the notation concise an abbreviation willbe introduced Suppose that 120574
119894 is a system of forms and 119894 119895
are integers then we make the abbreviation
120574119894119895plusmn
= 120574119894plusmn 119894120574119895 (46)
At this point quadratic pseudopotentials can be introducedin terms of the homogeneous variables of the same form as
6 International Journal of Mathematics and Mathematical Sciences
(30) In the same way that (31) was produced the followingPfaffian equations based on the set 120572
1198943
1in (44) are obtained
1205724= 1198891199104minus 12059612+
+ 211991041205963+ 1199102
412059612minus
minus 119910512059667minus
+ 1199104119910512059645minus
1205725= 1198891199105minus 12059645+
+ 1199105(1205963+ radic3120596
8)
+ 1199102
512059645minus
minus 119910412059667+
+ 1199104119910512059612minus
1205726= 1198891199106minus 12059612minus
minus 211991061205963+ 1199102
612059612+
minus 119910712059645minus
+ 1199106119910712059667minus
1205727= 1198891199107minus 12059667+
minus 1199107(1205963minus radic3120596
8)
+ 1199102
712059667minus
minus 119910612059645+
+ 1199106119910712059612+
1205728= 1198891199108minus 12059645minus
minus 1199108(1205963+ radic3120596
8)
+ 1199102
812059645+
minus 119910912059612minus
+ 1199108119910912059667+
1205729= 1198891199109minus 12059667minus
+ 1199109(1205963minus radic3120596
8)
+ 1199102
912059667+
minus 119910812059612+
+ 1199108119910912059645+
(47)
These are coupledRiccati equations for the pairs of pseudopo-tentials (119910
4 1199105) (1199106 1199107) and (119910
8 1199109) respectively
Define the following set of 2 times 2matrices of one formsΩ119894
for 119894 = 1 2 3 as
Ω1=(minus21205963minus2119910412059612minusminus119910512059645minus 12059667minusminus119910412059645minus
12059667+minus119910512059612minus minus1205963minusradic31205968minus119910412059612minusminus2119910512059645minus
)
Ω2=(21205963minus2119910612059612+ minus 119910712059667minus 12059645minusminus119910612059667minus
12059645+minus119910712059612+ 1205963minusradic31205968minus119910612059612+minus2119910712059667minus
)
Ω3=(1205963+radic31205968minus2119910812059645+minus119910912059667+ 12059612minusminus119910812059667+
12059612+minus119910912059645+ minus1205963+radic31205968minus119910812059645+minus2119910912059667+
)
(48)
Making use of the matrices Ω119894defined in (48) the following
result can be stated
Theorem 11 The closure properties of the set of forms 1205721198949
4
given by (47) can be expressed in terms of the Ω119894as follows
119889(12057241205725)
= ((1199102
4minus 1) 1205991minus119894 (119910
2
4+ 1) 1205992+211991041205993+1199104119910512059945minusminus119910512059967minus
1199104119910512059912minus+11991051205993+(1199102
4minus 1) 1205994minus119894 (119910
2
5+ 1) 1205995minus119910412059967++
radic311991051205998
)
+Ω1 and (12057241205725)
119889 (12057261205727)
= ((1199102
6minus 1) 1205991+119894 (119910
2
6+ 1) 1205992minus211991061205993minus119910712059945minus+1199106119910712059967minus
1199106119910712059912+minus11991071205993minus119910612059945++(1199102
7minus 1) 1205996minus119894 (119910
2
7+ 1) 1205997+
radic311991071205998
)
+Ω2 and (12057261205727)
119889 (12057281205729)
= (minus119910912059912minusminus11991081205993+(119910
2
8minus 1) 1205994+119894 (119910
2
8+ 1) 1205995+1199108119910912059967+minus
radic311991081205998
minus119910812059912++11991091205993+1199108119910912059945++(1199102
9minus 1) 1205996+119894 (119910
2
9+ 1) 1205997minus
radic311991091205998
)
+Ω3 and (12057281205729)
(49)
Based on the forms Ω119894given in (48) we can differentiate
to define the following matrices of two forms 120585119894given by
120585119894= 119889Ω119894minus Ω119894and Ω119894 (50)
Theorem 12 The forms 120585119894defined in (50) are given explicitly
by the matrices
1205851
=(
212059612+ and 1205724+12059645minus and 1205725 12059645minus and 1205724minus119910412059945minus+12059967minus
minus2119910412059912minus minus 21205993 minus 119910512059945minus12059612minus and 1205724+212059645minus and 1205725
12059612minus and 1205725minus119910512059912minus+12059967+ minus119910412059912minusminus1205993 minus 212059945minus minusradic31205998
)
1205852
=(
212059612+ and 1205726+12059667minus and 1205727 12059667minus and 1205726+12059945minus minus 119910612059967minus
minus2119910612059912+ + 1205993 minus 119910712059967minus12059612+ and 1205726+212059667minus and 1205727minus119910612059912+
12059612+ and 1205727 minus 1199107 12059912+ + 12059945+ +1205993 minus 2119910712059967minus minusradic31205998
)
1205853
=(
212059645+ and 1205728+12059667+ and 1205729+1205993 12059667+ and 1205728+12059912minusminus119910812059967+
minus2119910812059945+ minus 119910912059967+ +radic3120599812059645+ and 1205728+212059667+ and 1205729minus1205993
12059645+ and 1205729+12059912+minus119910912059945+ minus119910812059945+ minus 2119910912059967+ +radic31205998
)
(51)
From these results it is concluded that 1205851is contained in
the ring of 1205724 1205725 and the 120599
119897 1205852is contained in the ring of
1205726 1205727 and 120599
119897 and 120585
3is in the ring of 120572
8 1205729 and 120599
119897
The two forms 1205851198943
1therefore vanish for the solutions of the
nonlinear equations (39) and of the coupled Riccati equations120572119895= 09
4 As in the case of 119874(3) the one forms Ω
119894are not
traceless Denoting the trace of Ω119894by
120591119894= trΩ
119894 (52)
the following theorem then follows
Theorem 13 The closure properties of the exterior derivativesof the traces 120591
119894are given by
1
31198891205911= 12059612minus
and 1205724+ 12059645minus
and 1205725
minus 119910412059912minus
minus 1205993minus 119910512059945minus
minus1
radic3
1205998
International Journal of Mathematics and Mathematical Sciences 7
1
31198891205912= 12059612+
and 1205726+ 12059667minus
and 1205727
minus 119910612059912+
+ 1205993minus 119910712059967minus
minus1
radic3
1205998
1
31198891205913= 12059645+
and 1205728+ 12059667+
and 1205729
minus 119910812059945+
minus 119910912059967+
+2
radic3
1205998
(53)
The one forms (52) then can be used to generate con-servation laws Note that as in the 119874(3) case a 3 times 3
problemΩ has been reduced to three separate 2times2 problemsin terms of the matrices Ω
119897 Further prolongation can be
continued beginning with the one formsΩ119897given in (48) To
briefly outline the further steps in the procedure a system ofPfaffians
119897119895 is introduced which are based on the one forms
Ω119897
119897119895= 0
119897119895= 119889119910119897119895minus (Ω119897)119895119896119910119897119896 (54)
The subscript 119897 in 119910119897119895and
119897119895indicates that they belong to the
subsystem defined byΩ119897 and it is not summed over Exterior
differentiation of 119897119895yields
119889119897119895= (Ω119897)119895119896and 119897119896minus (Θ)
119895119896119910119897119896 (55)
The 119910119897119895 are pseudopotentials for the original nonlinear
equation (39) Next quadratic pseudopotentials are includedas the homogeneous variables and the prolongation can becontinued
5 A Conservation Law and Summary
These types of results turn out to be very useful for furtherstudy of integrable equationsThey can be used for generatinginfinite numbers of conservation laws In addition the resultsare independent of any further structure of the forms 120596
119894in
all cases In fact the one form Ω need not be thought of asuniqueThis is due to the fact thatΩ andΘ are form invariantunder the gauge transformationΩ rarr 120596
1015840= 119889119860 119860
minus1+119860Ω119860
minus1
and Θ rarr Θ1015840= 119860Θ119860
minus1 where in the 119878119871(2R) case 119860 is anarbitrary 2 times 2 space-time-dependent matrix of determinantone The gauge transformation property holds in the 3 times 3
case as well The pseudopotentials serve as potentials forconservation laws in a generalized senseThey can be definedunder a choice of Pfaffian forms such as
120572119894= 0 120572
119894= 119889119910119894+ 119865119894119889119909 + 119866
119894119889119905 (56)
with the property that the exterior derivatives 119889120572119894are con-
tained in the ring spanned by 120572119894 and 120599
119897
119889120572119894= sum
119895
119860119894119895and 120572119895+sum
119897
Γ119894119897120599119897 (57)
This can be thought of as a generalization of the FrobeniusTheorem for complete integrability of Pfaffian systems
Theorem 3 implies that 119889120590119894= 0when 119894 = 1 2 for solutions
of the original equation If either of these forms is expressedas 120590 = I119889119909 +J119889119905 then 119889120590 = 0 implies that
120597I
120597119905minus120597J
120597119905= 0 (58)
ThusI is a conserved density andJ a conserved current Letus finally represent 120596
1= 1198861119889119909 + 119887
1119889119905 1205962= 1198862119889119909 + 119887
2119889119905 and
1205963= 120578119889119909 + 119887
3119889119905 where 120578 is a parameter The 119909-dependent
piece of 1205723in (17) implies
1199103119909
+ 211988611199103+ 11988621199102
3minus 120578 = 0 (59)
By substituting an asymptotic expansion around 120578 = infin for1199103in (59) of the form
1199103=
infin
sum
0
120578minus119899119884119899 (60)
a recursion for the 119884119899is obtained Thus (59) becomes
sum
119899
120578minus119899119884119899119909
+ 21198861sum
119899
120578minus119899119884119899
+ 1198862(sum
119899
120578minus119899119884119899)
2
minus 120578 = 0
(61)
Expanding the power collecting coefficients of 120578 and equat-ing coefficients of 120578 to zero we get
1198841119909
+ 211988611198841= 1 119884
119899119909+ 21198861119884119899+ 1198862
119899minus1
sum
119896=1
119884119899minus119896
119884119896= 0
(62)
The consistency of solving 1205723by using just the 119909 part is
guaranteed by complete integrability The 119909 part of the form1205901is expressed as
(1205901)119909= (1198861+
infin
sum
119899=1
120578minus1198991198841198991198862)119889119909 (63)
Consequently from (58) the 119899th conserved density is
I119899= 1198862119884119899 (64)
The existence of links between the types of prolongationhere and other types of prolongations which are based onclosed differential systems is a subject for further work
References
[1] F B Estabrook and H D Wahlquist ldquoClassical geometriesdefined by exterior differential systems on higher frame bun-dlesrdquo Classical and Quantum Gravity vol 6 no 3 pp 263ndash2741989
[2] H Cartan Differential Forms Dover Mineola NY USA 2006[3] M J Ablowitz D J Kaup A C Newell and H Segur ldquoMethod
for solving the sine-Gordon equationrdquo Physical Review Lettersvol 30 pp 1262ndash1264 1973
8 International Journal of Mathematics and Mathematical Sciences
[4] M J Ablowitz D K Kaup A C Newell and H SegurldquoNonlinear-evolution equations of physical significancerdquo Phys-ical Review Letters vol 31 pp 125ndash127 1973
[5] R Sasaki ldquoPseudopotentials for the general AKNS systemrdquoPhysics Letters A vol 73 no 2 pp 77ndash80 1979
[6] R Sasaki ldquoGeometric approach to soliton equationsrdquo Proceed-ings of the Royal Society London vol 373 no 1754 pp 373ndash3841980
[7] M Crampin ldquoSolitons and 119878119871(2R)rdquo Physics Letters A vol 66no 3 pp 170ndash172 1978
[8] D J Kaup and J Yang ldquoThe inverse scattering transform andsquared eigenfunctions for a degenerate 3 times 3 operatorrdquo InverseProblems vol 25 no 10 Article ID 105010 2009
[9] D J Kaup and R A Van Gorder ldquoThe inverse scatteringtransform and squared eigenfunctions for the nondegenerate3 times 3 operator and its soliton structurerdquo Inverse Problems vol26 no 5 Article ID 055005 2010
[10] P Bracken ldquoIntrinsic formulation of geometric integrabilityand associated Riccati system generating conservation lawsrdquoInternational Journal of Geometric Methods in Modern Physicsvol 6 no 5 pp 825ndash837 2009
[11] D J Kaup and R A Van Gorder ldquoSquared eigenfunctions andthe perturbation theory for the nondegenerate N timesN operatora general outlinerdquo Journal of Physics A vol 43 Article ID434019 2010
[12] H D Wahlquist and F B Estabrook ldquoProlongation structuresof nonlinear evolution equationsrdquo Journal of MathematicalPhysics vol 16 pp 1ndash7 1975
[13] P Bracken ldquoOn two-dimensional manifolds with constantGaussian curvature and their associated equationsrdquo Interna-tional Journal of Geometric Methods in Modern Physics vol 9no 3 Article ID 1250018 2012
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
6 International Journal of Mathematics and Mathematical Sciences
(30) In the same way that (31) was produced the followingPfaffian equations based on the set 120572
1198943
1in (44) are obtained
1205724= 1198891199104minus 12059612+
+ 211991041205963+ 1199102
412059612minus
minus 119910512059667minus
+ 1199104119910512059645minus
1205725= 1198891199105minus 12059645+
+ 1199105(1205963+ radic3120596
8)
+ 1199102
512059645minus
minus 119910412059667+
+ 1199104119910512059612minus
1205726= 1198891199106minus 12059612minus
minus 211991061205963+ 1199102
612059612+
minus 119910712059645minus
+ 1199106119910712059667minus
1205727= 1198891199107minus 12059667+
minus 1199107(1205963minus radic3120596
8)
+ 1199102
712059667minus
minus 119910612059645+
+ 1199106119910712059612+
1205728= 1198891199108minus 12059645minus
minus 1199108(1205963+ radic3120596
8)
+ 1199102
812059645+
minus 119910912059612minus
+ 1199108119910912059667+
1205729= 1198891199109minus 12059667minus
+ 1199109(1205963minus radic3120596
8)
+ 1199102
912059667+
minus 119910812059612+
+ 1199108119910912059645+
(47)
These are coupledRiccati equations for the pairs of pseudopo-tentials (119910
4 1199105) (1199106 1199107) and (119910
8 1199109) respectively
Define the following set of 2 times 2matrices of one formsΩ119894
for 119894 = 1 2 3 as
Ω1=(minus21205963minus2119910412059612minusminus119910512059645minus 12059667minusminus119910412059645minus
12059667+minus119910512059612minus minus1205963minusradic31205968minus119910412059612minusminus2119910512059645minus
)
Ω2=(21205963minus2119910612059612+ minus 119910712059667minus 12059645minusminus119910612059667minus
12059645+minus119910712059612+ 1205963minusradic31205968minus119910612059612+minus2119910712059667minus
)
Ω3=(1205963+radic31205968minus2119910812059645+minus119910912059667+ 12059612minusminus119910812059667+
12059612+minus119910912059645+ minus1205963+radic31205968minus119910812059645+minus2119910912059667+
)
(48)
Making use of the matrices Ω119894defined in (48) the following
result can be stated
Theorem 11 The closure properties of the set of forms 1205721198949
4
given by (47) can be expressed in terms of the Ω119894as follows
119889(12057241205725)
= ((1199102
4minus 1) 1205991minus119894 (119910
2
4+ 1) 1205992+211991041205993+1199104119910512059945minusminus119910512059967minus
1199104119910512059912minus+11991051205993+(1199102
4minus 1) 1205994minus119894 (119910
2
5+ 1) 1205995minus119910412059967++
radic311991051205998
)
+Ω1 and (12057241205725)
119889 (12057261205727)
= ((1199102
6minus 1) 1205991+119894 (119910
2
6+ 1) 1205992minus211991061205993minus119910712059945minus+1199106119910712059967minus
1199106119910712059912+minus11991071205993minus119910612059945++(1199102
7minus 1) 1205996minus119894 (119910
2
7+ 1) 1205997+
radic311991071205998
)
+Ω2 and (12057261205727)
119889 (12057281205729)
= (minus119910912059912minusminus11991081205993+(119910
2
8minus 1) 1205994+119894 (119910
2
8+ 1) 1205995+1199108119910912059967+minus
radic311991081205998
minus119910812059912++11991091205993+1199108119910912059945++(1199102
9minus 1) 1205996+119894 (119910
2
9+ 1) 1205997minus
radic311991091205998
)
+Ω3 and (12057281205729)
(49)
Based on the forms Ω119894given in (48) we can differentiate
to define the following matrices of two forms 120585119894given by
120585119894= 119889Ω119894minus Ω119894and Ω119894 (50)
Theorem 12 The forms 120585119894defined in (50) are given explicitly
by the matrices
1205851
=(
212059612+ and 1205724+12059645minus and 1205725 12059645minus and 1205724minus119910412059945minus+12059967minus
minus2119910412059912minus minus 21205993 minus 119910512059945minus12059612minus and 1205724+212059645minus and 1205725
12059612minus and 1205725minus119910512059912minus+12059967+ minus119910412059912minusminus1205993 minus 212059945minus minusradic31205998
)
1205852
=(
212059612+ and 1205726+12059667minus and 1205727 12059667minus and 1205726+12059945minus minus 119910612059967minus
minus2119910612059912+ + 1205993 minus 119910712059967minus12059612+ and 1205726+212059667minus and 1205727minus119910612059912+
12059612+ and 1205727 minus 1199107 12059912+ + 12059945+ +1205993 minus 2119910712059967minus minusradic31205998
)
1205853
=(
212059645+ and 1205728+12059667+ and 1205729+1205993 12059667+ and 1205728+12059912minusminus119910812059967+
minus2119910812059945+ minus 119910912059967+ +radic3120599812059645+ and 1205728+212059667+ and 1205729minus1205993
12059645+ and 1205729+12059912+minus119910912059945+ minus119910812059945+ minus 2119910912059967+ +radic31205998
)
(51)
From these results it is concluded that 1205851is contained in
the ring of 1205724 1205725 and the 120599
119897 1205852is contained in the ring of
1205726 1205727 and 120599
119897 and 120585
3is in the ring of 120572
8 1205729 and 120599
119897
The two forms 1205851198943
1therefore vanish for the solutions of the
nonlinear equations (39) and of the coupled Riccati equations120572119895= 09
4 As in the case of 119874(3) the one forms Ω
119894are not
traceless Denoting the trace of Ω119894by
120591119894= trΩ
119894 (52)
the following theorem then follows
Theorem 13 The closure properties of the exterior derivativesof the traces 120591
119894are given by
1
31198891205911= 12059612minus
and 1205724+ 12059645minus
and 1205725
minus 119910412059912minus
minus 1205993minus 119910512059945minus
minus1
radic3
1205998
International Journal of Mathematics and Mathematical Sciences 7
1
31198891205912= 12059612+
and 1205726+ 12059667minus
and 1205727
minus 119910612059912+
+ 1205993minus 119910712059967minus
minus1
radic3
1205998
1
31198891205913= 12059645+
and 1205728+ 12059667+
and 1205729
minus 119910812059945+
minus 119910912059967+
+2
radic3
1205998
(53)
The one forms (52) then can be used to generate con-servation laws Note that as in the 119874(3) case a 3 times 3
problemΩ has been reduced to three separate 2times2 problemsin terms of the matrices Ω
119897 Further prolongation can be
continued beginning with the one formsΩ119897given in (48) To
briefly outline the further steps in the procedure a system ofPfaffians
119897119895 is introduced which are based on the one forms
Ω119897
119897119895= 0
119897119895= 119889119910119897119895minus (Ω119897)119895119896119910119897119896 (54)
The subscript 119897 in 119910119897119895and
119897119895indicates that they belong to the
subsystem defined byΩ119897 and it is not summed over Exterior
differentiation of 119897119895yields
119889119897119895= (Ω119897)119895119896and 119897119896minus (Θ)
119895119896119910119897119896 (55)
The 119910119897119895 are pseudopotentials for the original nonlinear
equation (39) Next quadratic pseudopotentials are includedas the homogeneous variables and the prolongation can becontinued
5 A Conservation Law and Summary
These types of results turn out to be very useful for furtherstudy of integrable equationsThey can be used for generatinginfinite numbers of conservation laws In addition the resultsare independent of any further structure of the forms 120596
119894in
all cases In fact the one form Ω need not be thought of asuniqueThis is due to the fact thatΩ andΘ are form invariantunder the gauge transformationΩ rarr 120596
1015840= 119889119860 119860
minus1+119860Ω119860
minus1
and Θ rarr Θ1015840= 119860Θ119860
minus1 where in the 119878119871(2R) case 119860 is anarbitrary 2 times 2 space-time-dependent matrix of determinantone The gauge transformation property holds in the 3 times 3
case as well The pseudopotentials serve as potentials forconservation laws in a generalized senseThey can be definedunder a choice of Pfaffian forms such as
120572119894= 0 120572
119894= 119889119910119894+ 119865119894119889119909 + 119866
119894119889119905 (56)
with the property that the exterior derivatives 119889120572119894are con-
tained in the ring spanned by 120572119894 and 120599
119897
119889120572119894= sum
119895
119860119894119895and 120572119895+sum
119897
Γ119894119897120599119897 (57)
This can be thought of as a generalization of the FrobeniusTheorem for complete integrability of Pfaffian systems
Theorem 3 implies that 119889120590119894= 0when 119894 = 1 2 for solutions
of the original equation If either of these forms is expressedas 120590 = I119889119909 +J119889119905 then 119889120590 = 0 implies that
120597I
120597119905minus120597J
120597119905= 0 (58)
ThusI is a conserved density andJ a conserved current Letus finally represent 120596
1= 1198861119889119909 + 119887
1119889119905 1205962= 1198862119889119909 + 119887
2119889119905 and
1205963= 120578119889119909 + 119887
3119889119905 where 120578 is a parameter The 119909-dependent
piece of 1205723in (17) implies
1199103119909
+ 211988611199103+ 11988621199102
3minus 120578 = 0 (59)
By substituting an asymptotic expansion around 120578 = infin for1199103in (59) of the form
1199103=
infin
sum
0
120578minus119899119884119899 (60)
a recursion for the 119884119899is obtained Thus (59) becomes
sum
119899
120578minus119899119884119899119909
+ 21198861sum
119899
120578minus119899119884119899
+ 1198862(sum
119899
120578minus119899119884119899)
2
minus 120578 = 0
(61)
Expanding the power collecting coefficients of 120578 and equat-ing coefficients of 120578 to zero we get
1198841119909
+ 211988611198841= 1 119884
119899119909+ 21198861119884119899+ 1198862
119899minus1
sum
119896=1
119884119899minus119896
119884119896= 0
(62)
The consistency of solving 1205723by using just the 119909 part is
guaranteed by complete integrability The 119909 part of the form1205901is expressed as
(1205901)119909= (1198861+
infin
sum
119899=1
120578minus1198991198841198991198862)119889119909 (63)
Consequently from (58) the 119899th conserved density is
I119899= 1198862119884119899 (64)
The existence of links between the types of prolongationhere and other types of prolongations which are based onclosed differential systems is a subject for further work
References
[1] F B Estabrook and H D Wahlquist ldquoClassical geometriesdefined by exterior differential systems on higher frame bun-dlesrdquo Classical and Quantum Gravity vol 6 no 3 pp 263ndash2741989
[2] H Cartan Differential Forms Dover Mineola NY USA 2006[3] M J Ablowitz D J Kaup A C Newell and H Segur ldquoMethod
for solving the sine-Gordon equationrdquo Physical Review Lettersvol 30 pp 1262ndash1264 1973
8 International Journal of Mathematics and Mathematical Sciences
[4] M J Ablowitz D K Kaup A C Newell and H SegurldquoNonlinear-evolution equations of physical significancerdquo Phys-ical Review Letters vol 31 pp 125ndash127 1973
[5] R Sasaki ldquoPseudopotentials for the general AKNS systemrdquoPhysics Letters A vol 73 no 2 pp 77ndash80 1979
[6] R Sasaki ldquoGeometric approach to soliton equationsrdquo Proceed-ings of the Royal Society London vol 373 no 1754 pp 373ndash3841980
[7] M Crampin ldquoSolitons and 119878119871(2R)rdquo Physics Letters A vol 66no 3 pp 170ndash172 1978
[8] D J Kaup and J Yang ldquoThe inverse scattering transform andsquared eigenfunctions for a degenerate 3 times 3 operatorrdquo InverseProblems vol 25 no 10 Article ID 105010 2009
[9] D J Kaup and R A Van Gorder ldquoThe inverse scatteringtransform and squared eigenfunctions for the nondegenerate3 times 3 operator and its soliton structurerdquo Inverse Problems vol26 no 5 Article ID 055005 2010
[10] P Bracken ldquoIntrinsic formulation of geometric integrabilityand associated Riccati system generating conservation lawsrdquoInternational Journal of Geometric Methods in Modern Physicsvol 6 no 5 pp 825ndash837 2009
[11] D J Kaup and R A Van Gorder ldquoSquared eigenfunctions andthe perturbation theory for the nondegenerate N timesN operatora general outlinerdquo Journal of Physics A vol 43 Article ID434019 2010
[12] H D Wahlquist and F B Estabrook ldquoProlongation structuresof nonlinear evolution equationsrdquo Journal of MathematicalPhysics vol 16 pp 1ndash7 1975
[13] P Bracken ldquoOn two-dimensional manifolds with constantGaussian curvature and their associated equationsrdquo Interna-tional Journal of Geometric Methods in Modern Physics vol 9no 3 Article ID 1250018 2012
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
International Journal of Mathematics and Mathematical Sciences 7
1
31198891205912= 12059612+
and 1205726+ 12059667minus
and 1205727
minus 119910612059912+
+ 1205993minus 119910712059967minus
minus1
radic3
1205998
1
31198891205913= 12059645+
and 1205728+ 12059667+
and 1205729
minus 119910812059945+
minus 119910912059967+
+2
radic3
1205998
(53)
The one forms (52) then can be used to generate con-servation laws Note that as in the 119874(3) case a 3 times 3
problemΩ has been reduced to three separate 2times2 problemsin terms of the matrices Ω
119897 Further prolongation can be
continued beginning with the one formsΩ119897given in (48) To
briefly outline the further steps in the procedure a system ofPfaffians
119897119895 is introduced which are based on the one forms
Ω119897
119897119895= 0
119897119895= 119889119910119897119895minus (Ω119897)119895119896119910119897119896 (54)
The subscript 119897 in 119910119897119895and
119897119895indicates that they belong to the
subsystem defined byΩ119897 and it is not summed over Exterior
differentiation of 119897119895yields
119889119897119895= (Ω119897)119895119896and 119897119896minus (Θ)
119895119896119910119897119896 (55)
The 119910119897119895 are pseudopotentials for the original nonlinear
equation (39) Next quadratic pseudopotentials are includedas the homogeneous variables and the prolongation can becontinued
5 A Conservation Law and Summary
These types of results turn out to be very useful for furtherstudy of integrable equationsThey can be used for generatinginfinite numbers of conservation laws In addition the resultsare independent of any further structure of the forms 120596
119894in
all cases In fact the one form Ω need not be thought of asuniqueThis is due to the fact thatΩ andΘ are form invariantunder the gauge transformationΩ rarr 120596
1015840= 119889119860 119860
minus1+119860Ω119860
minus1
and Θ rarr Θ1015840= 119860Θ119860
minus1 where in the 119878119871(2R) case 119860 is anarbitrary 2 times 2 space-time-dependent matrix of determinantone The gauge transformation property holds in the 3 times 3
case as well The pseudopotentials serve as potentials forconservation laws in a generalized senseThey can be definedunder a choice of Pfaffian forms such as
120572119894= 0 120572
119894= 119889119910119894+ 119865119894119889119909 + 119866
119894119889119905 (56)
with the property that the exterior derivatives 119889120572119894are con-
tained in the ring spanned by 120572119894 and 120599
119897
119889120572119894= sum
119895
119860119894119895and 120572119895+sum
119897
Γ119894119897120599119897 (57)
This can be thought of as a generalization of the FrobeniusTheorem for complete integrability of Pfaffian systems
Theorem 3 implies that 119889120590119894= 0when 119894 = 1 2 for solutions
of the original equation If either of these forms is expressedas 120590 = I119889119909 +J119889119905 then 119889120590 = 0 implies that
120597I
120597119905minus120597J
120597119905= 0 (58)
ThusI is a conserved density andJ a conserved current Letus finally represent 120596
1= 1198861119889119909 + 119887
1119889119905 1205962= 1198862119889119909 + 119887
2119889119905 and
1205963= 120578119889119909 + 119887
3119889119905 where 120578 is a parameter The 119909-dependent
piece of 1205723in (17) implies
1199103119909
+ 211988611199103+ 11988621199102
3minus 120578 = 0 (59)
By substituting an asymptotic expansion around 120578 = infin for1199103in (59) of the form
1199103=
infin
sum
0
120578minus119899119884119899 (60)
a recursion for the 119884119899is obtained Thus (59) becomes
sum
119899
120578minus119899119884119899119909
+ 21198861sum
119899
120578minus119899119884119899
+ 1198862(sum
119899
120578minus119899119884119899)
2
minus 120578 = 0
(61)
Expanding the power collecting coefficients of 120578 and equat-ing coefficients of 120578 to zero we get
1198841119909
+ 211988611198841= 1 119884
119899119909+ 21198861119884119899+ 1198862
119899minus1
sum
119896=1
119884119899minus119896
119884119896= 0
(62)
The consistency of solving 1205723by using just the 119909 part is
guaranteed by complete integrability The 119909 part of the form1205901is expressed as
(1205901)119909= (1198861+
infin
sum
119899=1
120578minus1198991198841198991198862)119889119909 (63)
Consequently from (58) the 119899th conserved density is
I119899= 1198862119884119899 (64)
The existence of links between the types of prolongationhere and other types of prolongations which are based onclosed differential systems is a subject for further work
References
[1] F B Estabrook and H D Wahlquist ldquoClassical geometriesdefined by exterior differential systems on higher frame bun-dlesrdquo Classical and Quantum Gravity vol 6 no 3 pp 263ndash2741989
[2] H Cartan Differential Forms Dover Mineola NY USA 2006[3] M J Ablowitz D J Kaup A C Newell and H Segur ldquoMethod
for solving the sine-Gordon equationrdquo Physical Review Lettersvol 30 pp 1262ndash1264 1973
8 International Journal of Mathematics and Mathematical Sciences
[4] M J Ablowitz D K Kaup A C Newell and H SegurldquoNonlinear-evolution equations of physical significancerdquo Phys-ical Review Letters vol 31 pp 125ndash127 1973
[5] R Sasaki ldquoPseudopotentials for the general AKNS systemrdquoPhysics Letters A vol 73 no 2 pp 77ndash80 1979
[6] R Sasaki ldquoGeometric approach to soliton equationsrdquo Proceed-ings of the Royal Society London vol 373 no 1754 pp 373ndash3841980
[7] M Crampin ldquoSolitons and 119878119871(2R)rdquo Physics Letters A vol 66no 3 pp 170ndash172 1978
[8] D J Kaup and J Yang ldquoThe inverse scattering transform andsquared eigenfunctions for a degenerate 3 times 3 operatorrdquo InverseProblems vol 25 no 10 Article ID 105010 2009
[9] D J Kaup and R A Van Gorder ldquoThe inverse scatteringtransform and squared eigenfunctions for the nondegenerate3 times 3 operator and its soliton structurerdquo Inverse Problems vol26 no 5 Article ID 055005 2010
[10] P Bracken ldquoIntrinsic formulation of geometric integrabilityand associated Riccati system generating conservation lawsrdquoInternational Journal of Geometric Methods in Modern Physicsvol 6 no 5 pp 825ndash837 2009
[11] D J Kaup and R A Van Gorder ldquoSquared eigenfunctions andthe perturbation theory for the nondegenerate N timesN operatora general outlinerdquo Journal of Physics A vol 43 Article ID434019 2010
[12] H D Wahlquist and F B Estabrook ldquoProlongation structuresof nonlinear evolution equationsrdquo Journal of MathematicalPhysics vol 16 pp 1ndash7 1975
[13] P Bracken ldquoOn two-dimensional manifolds with constantGaussian curvature and their associated equationsrdquo Interna-tional Journal of Geometric Methods in Modern Physics vol 9no 3 Article ID 1250018 2012
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
8 International Journal of Mathematics and Mathematical Sciences
[4] M J Ablowitz D K Kaup A C Newell and H SegurldquoNonlinear-evolution equations of physical significancerdquo Phys-ical Review Letters vol 31 pp 125ndash127 1973
[5] R Sasaki ldquoPseudopotentials for the general AKNS systemrdquoPhysics Letters A vol 73 no 2 pp 77ndash80 1979
[6] R Sasaki ldquoGeometric approach to soliton equationsrdquo Proceed-ings of the Royal Society London vol 373 no 1754 pp 373ndash3841980
[7] M Crampin ldquoSolitons and 119878119871(2R)rdquo Physics Letters A vol 66no 3 pp 170ndash172 1978
[8] D J Kaup and J Yang ldquoThe inverse scattering transform andsquared eigenfunctions for a degenerate 3 times 3 operatorrdquo InverseProblems vol 25 no 10 Article ID 105010 2009
[9] D J Kaup and R A Van Gorder ldquoThe inverse scatteringtransform and squared eigenfunctions for the nondegenerate3 times 3 operator and its soliton structurerdquo Inverse Problems vol26 no 5 Article ID 055005 2010
[10] P Bracken ldquoIntrinsic formulation of geometric integrabilityand associated Riccati system generating conservation lawsrdquoInternational Journal of Geometric Methods in Modern Physicsvol 6 no 5 pp 825ndash837 2009
[11] D J Kaup and R A Van Gorder ldquoSquared eigenfunctions andthe perturbation theory for the nondegenerate N timesN operatora general outlinerdquo Journal of Physics A vol 43 Article ID434019 2010
[12] H D Wahlquist and F B Estabrook ldquoProlongation structuresof nonlinear evolution equationsrdquo Journal of MathematicalPhysics vol 16 pp 1ndash7 1975
[13] P Bracken ldquoOn two-dimensional manifolds with constantGaussian curvature and their associated equationsrdquo Interna-tional Journal of Geometric Methods in Modern Physics vol 9no 3 Article ID 1250018 2012
Submit your manuscripts athttpwwwhindawicom
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MathematicsJournal of
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Mathematical Problems in Engineering
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Differential EquationsInternational Journal of
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Applied MathematicsJournal of
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Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Complex AnalysisJournal of
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OptimizationJournal of
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CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
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Operations ResearchAdvances in
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Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of