February 7, 2005 Lecture 7 - By Paul Lin 1 CPET 190 Lecture 7 Problem Solving with MATLAB Paul Lin lin

February 7, 2005February 7, 2005 Lecture 7 - By Paul LinLecture 7 - By Paul Lin 11

CPET 190 CPET 190

Lecture 7Lecture 7

Problem Solving with MATLABProblem Solving with MATLAB

Paul LinPaul Lin

http://www.etcs.ipfw.edu/~linhttp://www.etcs.ipfw.edu/~lin


Lecture 7: MATLAB Built-In FunctionsLecture 7: MATLAB Built-In Functions

7-1 Managing Variables and Workspace7-1 Managing Variables and Workspace

7-2 MATLAB Commands for Working with 7-2 MATLAB Commands for Working with Files and the Operating SystemFiles and the Operating System

7-3 Controlling Command Window7-3 Controlling Command Window

7-4 Time and Date Functions7-4 Time and Date Functions

7-5 Special Variables and Constants7-5 Special Variables and Constants


7-1 Managing Variables and 7-1 Managing Variables and WorkspaceWorkspace

Removing Unneeded VariablesRemoving Unneeded Variables• whowho - List current variables- List current variables• whoswhos - List current variables, long form- List current variables, long form• clearclear - Clear variables and functions- Clear variables and functions

Creating New VariablesCreating New Variables• lengthlength - Length of vector- Length of vector• sizesize - Size of matrix- Size of matrix

Saving to and Retrieving from Disk Files Saving to and Retrieving from Disk Files • load load - Retrieve variables from disks- Retrieve variables from disks• savesave - Save workspace variables to disk- Save workspace variables to disk• packpack - Consolidate workspace memory- Consolidate workspace memory

Workspace displayWorkspace display• dispdisp - Display matrix or text- Display matrix or text• fprintffprintf


7-1 Managing Variables and 7-1 Managing Variables and Workspace Workspace (continue)(continue)

Example 7-1: Example 7-1:

%cpet190_ex7_1.m%cpet190_ex7_1.mF = 4000;F = 4000;T = 1/F;T = 1/F;dt = 0.01*T;dt = 0.01*T;t = 0:dt:2*T;t = 0:dt:2*T;e1 = 5*sin(2*pi*F*t);e1 = 5*sin(2*pi*F*t);len = length(e1)len = length(e1)size_e1 = size(e1)size_e1 = size(e1)e2 = zeros(size(e1));e2 = zeros(size(e1));num = rand(2);num = rand(2);

fprintffprintf('The random number ('The random number array is %g\n', num);array is %g\n', num);fprintffprintf('\n');('\n');dispdisp('The random numbers');('The random numbers');dispdisp(num);(num);whoswhossave ex7_1save ex7_1clearclearload ex7_1load ex7_1whoswhos


7-1 Managing Variables and 7-1 Managing Variables and WorkspaceWorkspace

Example 7-1: OutputExample 7-1: Output


7-2 Working with Files and OS7-2 Working with Files and OS

The commands for working with files and The commands for working with files and operating systemoperating system

CommandCommand PurposePurpose

pwdpwd Show present working directoryShow present working directory

cdcd Change current working directoryChange current working directory

dirdir Directory listing (Window OS)Directory listing (Window OS)

lsls Directory Listing (Unix/Linux OS)Directory Listing (Unix/Linux OS)

deletedelete Delete fileDelete file

diarydiary Save text of MATLAB sessionSave text of MATLAB session

!! Execute OS commandsExecute OS commands


7-2 Working with Files and OS7-2 Working with Files and OS

Example 7-2Example 7-2

>> >> pwdpwdans =ans =C:\Courses\CPET190\C:\Courses\CPET190\

matlabex190matlabex190>> >> cd ..cd ..>> >> pwdpwdans =ans =C:\Courses\CPET190C:\Courses\CPET190>> >> dirdir. . Mlin_CPET190 Mlin_CPET190

.. .. ExsExsQuizQuiz LecturesLecturesMATLABExsMATLABExs

Example 7-2 (cont.)Example 7-2 (cont.)

>> >> diarydiary

>> diary off>> diary off

>> diary on>> diary on

>> >> !time!time

The current time is: The current time is: 11:31:05.02 11:31:05.02

Enter the new time: Enter the new time:

Open diary file using Open diary file using MATLAB M-file editor, MATLAB M-file editor, MS NOTEPAD, or MS MS NOTEPAD, or MS WordWord

helphelp


7-3 Controlling the Command 7-3 Controlling the Command WindowWindow

clcclc Clear command windowClear command windowhomehome Send cursor home (upper-left corner Send cursor home (upper-left corner

of command window)of command window)formatformat Set output formatSet output formatmoremore Control paged output in command Control paged output in command

windowwindowechoecho Echo on/off commands inside script Echo on/off commands inside script

files, for debugging purposesfiles, for debugging purposes



FunctionFunction PurposePurposedatedate CalendarCalendarclockclock System clock; accuracy 1/100th of a System clock; accuracy 1/100th of a

secondsecondnownow Current date and time as serial date Current date and time as serial date

numbernumberdatestrdatestr Convert a serial date number into the Convert a serial date number into the

common date/time, save as a string common date/time, save as a string cputimecputime How many seconds the MATLAB How many seconds the MATLAB

session is active; accuracy 1/100 th of session is active; accuracy 1/100 th of secondsecond

etimeetime Elapsed time functionElapsed time functiontictic Start watch timer functionStart watch timer functiontoctoc Stop watch timer functionStop watch timer function



Time and Date FunctionsTime and Date Functions

Example 7-3:Example 7-3:>>>> datedateans =ans =03-Oct-200403-Oct-2004>> >> nownowans =ans = 7.3222e+0057.3222e+005>> >> datestr(now)datestr(now)ans =ans =03-Oct-2004 12:47:2903-Oct-2004 12:47:29>> >> help datestrhelp datestr


7-4 Time and Date Functions 7-4 Time and Date Functions (continue)(continue)

CLOCK Current date and time as date vector.CLOCK Current date and time as date vector. CLOCK returns a six element date vector containing theCLOCK returns a six element date vector containing the current time and date in decimal form:current time and date in decimal form: CLOCK = [year month day hour minute seconds]CLOCK = [year month day hour minute seconds] The first five elements are integers. The seconds elementThe first five elements are integers. The seconds element is accurate to several digits beyond the decimal point.is accurate to several digits beyond the decimal point. FIX(CLOCK) rounds to integer display format.FIX(CLOCK) rounds to integer display format.

Example:Example:>>>> clockclockans =ans = 1.0e+003 *1.0e+003 * 2.0040 0.0100 0.0030 0.0120 0.0410 0.00712.0040 0.0100 0.0030 0.0120 0.0410 0.0071


7-4 Time and Date Functions 7-4 Time and Date Functions (continue)(continue)

Example 7-4 measuring program execution time Example 7-4 measuring program execution time (accuracy – 1/100 th of a second) using cputime (accuracy – 1/100 th of a second) using cputime functionfunction

t1_1 = cputime;t1_1 = cputime;for i =1:1000for i =1:1000 num_array = num_array = inv(rand(30));inv(rand(30));endendt1_2 = cputime;t1_2 = cputime;time_1000 = t1_2 - t1_1time_1000 = t1_2 - t1_1time_once = time_1000/1000time_once = time_1000/1000

time_1000 =time_1000 = 0.36100.3610

time_once =time_once = 3.6100e-0043.6100e-004



Example 7-5 measuring program execution time Example 7-5 measuring program execution time (accuracy – 1/100 th of a second) using tic and toc (accuracy – 1/100 th of a second) using tic and toc functionsfunctions

tic;for i =1:1000 num_array = inv(rand(30));endtoc

elapsed_time =elapsed_time = 0.36100.3610


7-5 Special Variables and Constants7-5 Special Variables and Constants

Example 7-6: AC circuit Example 7-6: AC circuit calculation using calculation using complex numbers.complex numbers.

A RLC circuit is shown on A RLC circuit is shown on this slide, findthis slide, find

a)a) Total impedance ZTotal impedance Z

b)b) Voltage and current Voltage and current across each components across each components

10 V 60HzSine wave

R = 8 ohms

XL = j 6 ohms

Xc = - j2 ohms


7-5 Special Variables and Constants 7-5 Special Variables and Constants (continue)(continue)

Example 7-6: Example 7-6: Analysis: Domain knowledgeAnalysis: Domain knowledge XL = 2XL = 2ππfLfL, where L is the , where L is the

inductance in Henry, f is the inductance in Henry, f is the frequency of ac sourcefrequency of ac source

XC = 1/(2 XC = 1/(2 ππfC)fC), where C is the , where C is the capacitance in Farardcapacitance in Farard

Z = R + j(XL – XC) Z = R + j(XL – XC) -- total -- total impedance, where j shows impedance, where j shows the imaginary component of the imaginary component of a complex number a complex number

I = E/ZI = E/Z, total current, total current VR = I*RVR = I*R, voltage drop across , voltage drop across

resistorresistor VL = I*XLVL = I*XL, voltage drop , voltage drop

across the inductoracross the inductor VC = I*XCVC = I*XC voltage drop voltage drop

across the capacitoracross the capacitor

10 V 60HzSine wave

R = 8 ohms

XL = j 6 ohms

Xc = - j2 ohms



Example 7-6: MATLAB Example 7-6: MATLAB Program Program

%RLC_1.m%RLC_1.mf = 60; R = 8;f = 60; R = 8;% Peak value of the sine wave% Peak value of the sine wavee = 10;e = 10;XL = j*6; XC = -j*2;XL = j*6; XC = -j*2;Z = R + (XL+XC)Z = R + (XL+XC)theta = angle(Z)theta = angle(Z) % 0.4636 pi% 0.4636 pi% 180 pi% 180 pi% ----- = ----% ----- = ----% theta_degree theta% theta_degree thetatheta_degree = (180*theta)/pitheta_degree = (180*theta)/pi% 26.5615 degree = 0.4636 pi% 26.5615 degree = 0.4636 pimag_Z = abs(Z)mag_Z = abs(Z)

Real Axis

Imaginary Axis

J

R = 8 ohms

XL = j6 ohms

XC = -j2 ohms

Theta



Example 7-6:Example 7-6: MATLAB Program (cont.)MATLAB Program (cont.)%RLC_1.m %RLC_1.m %%I = e/ZI = e/ZI_thea_degree = angle(I) * I_thea_degree = angle(I) *

(180)/pi(180)/piI_mag = abs(I)I_mag = abs(I)VR = I*RVR = I*RVL = I*XLVL = I*XLVC = I*XCVC = I*XCVR + (VL + VC)% e = 10 voltVR + (VL + VC)% e = 10 volt

VR =VR = 8.0000 - 4.0000i8.0000 - 4.0000iVL =VL = 3.0000 + 6.0000i3.0000 + 6.0000iVC =VC = -1.0000 - 2.0000i-1.0000 - 2.0000i>> VR + (VL + VC)>> VR + (VL + VC)ans =ans = 1010


SummarySummary

Managing Variables and WorkspaceManaging Variables and Workspace MATLAB Commands for Working with MATLAB Commands for Working with

Files and the Operating SystemFiles and the Operating System Controlling Command WindowsControlling Command Windows Date and Time FunctionsDate and Time Functions Special Variables and ConstantsSpecial Variables and Constants


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February 7, 2005 Lecture 7 - By Paul Lin 1 CPET 190 Lecture 7 Problem Solving with MATLAB Paul Lin lin