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CDB 4333Z – PROCESS OPTIMIZATION LINEAR PROGRAMMING ZULFAN ADI PUTRA, PDENG OFFICE: 05-03-08 TELP: 05 368 7562 EMAIL: Z [email protected] DISCUSSION TIME: FRIDAY , 15.00-18.00 1 Open

Chemical Engineering Department · 2020. 5. 7. · Degenerate linear programming (LP) problems 4. Simplex method 5. Sensitivity analysis 6. ... Price = 24 USD/bbl Crude 2 Price =

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  • CDB 4333Z – PROCESS OPTIMIZATION

    LINEAR PROGRAMMING

    ZULFAN ADI PUTRA, PDENG

    OFFICE: 05-03-08TELP: 05 368 7562

    EMAIL: [email protected] TIME: FRIDAY, 15.00-18.00

    1Open

    mailto:[email protected]

  • 2

    Objective and Constraints formulation

    Multi variable

    One variable

    Unconstrained optimization

    Constrained Optimization

    Methods:• Function value,

    • Bracketing,• Newton,• Secant

    Methods:• Simplex,• Newton,• Steepest

    descentLagrange multiplier

    and Karush Kuhn Tucker algorithm

    Linear programming via Simplex method

    Non Linear programming

    Methods:• SQP,• GRG,

    • PenaltyInteger programming via Branch and Bound

    COURSE OVERVIEW

    Open

  • 3

    COURSE OUTCOME

    Open

  • 1. Refinery case: Problem formulation

    2. Graphical solution for two variable problems

    3. Degenerate linear programming (LP) problems

    4. Simplex method

    5. Sensitivity analysis

    6. Duality in LP

    4

    CONTENTS

    Open

  • 5

    GENERAL FEATURES

    ▪Linear Programming (LP)→most widely used in chemical industry

    ▪LP implies that objective function and all constraints are linear

    ▪LP problems are convex programming, where:

    •the objective function is convex (linear) and

    •the constraints form a convex region or solution space

    The solution isglobal optimum

    The basic steps involved in formulating an LP model are:

    1) Identify decision variables

    2) Express constraints as linear equalities or inequalities

    3) Write the objective function as a linear function

    Open

  • Product Volume Percent Yield Max allowable production

    Crude 1 Crude 2 (bbl/day)

    Gasoline 80 44 24000

    Kerosene 5 10 2000

    Fuel Oil 10 36 6000

    Residues 5 10

    Processing cost (USD/bbl) 0.5 1

    6

    REFINERY PRODUCTION PLANNING

    Refinery

    Crude 1Price = 24 USD/bbl

    Crude 2Price = 15 USD/bbl

    Gasoline, Price = 36 USD/bblKerosene, Price = 24 USD/bblFuel Oil, Price = 21 USD/bblResidues, Price = 10 USD/bbl

    Two different crudes are available to be refined. The objective is to maximize the profit

    Open

  • ▪ Your company has two plants, which are in Barcelona and Antwerp,and three market hubs, located in Rotterdam, Frankfurt, and Porto. Thedistances between the plants and the markets, together with thecapacities and demands of each hub are shown in TABLE Q1. Thetransportation cost is 10 RM/ton∙km.

    ▪ Determine the amount of goods that has to be transported fromeach plant to each market hub to minimize the total cost oftransportation

    7

    MARKET AND DEMAND PROBLEM

    Open

  • ▪ Your company just bought two lubricant factories as subsidiary companies.Until now, they are only selling the lubricants via historical partnershipwith their customers. Apparently, they have two same customers.

    ▪ This situation does not make the new supply chain manager happy. So, hecalls you as the recommended senior process engineer within the company.

    ▪ He tells you that the 1st factory has 400 tons of lubricants in their storage,while the other has 300 tons. The 1st customer needs 200 tons oflubricants, while the other requires 300 tons. The supply chain managershows you the cost of shipments ($/ton) as shown below.

    ▪ Then, he asks for your advice on how much lubricant from each factoryshould be sent to each customer. What are you going to say?

    8

    CUSTOMER PROBLEM (AND MANY MORE LP…)

    Customer 1 Customer 2

    Factory 1 $ 30 $ 25

    Factory 2 $ 36 $ 30

    Open

  • Product Volume Percent Yield Max allowable production

    Crude 1 Crude 2 (bbl/day)

    Gasoline 80 44 24000

    Kerosene 5 10 2000

    Fuel Oil 10 36 6000

    Residues 5 10

    Processing cost (USD/bbl) 0.5 1

    9

    OPENING QUESTION: FORMULATE THE OPTIMIZATION PROBLEM

    Refinery

    Crude 1Price = 24 USD/bbl

    Crude 2Price = 15 USD/bbl

    Gasoline, Price = 36 USD/bblKerosene, Price = 24 USD/bblFuel Oil, Price = 21 USD/bblResidues, Price = 10 USD/bbl

    Two different crudes are available to be refined. The objective is to maximize the profit

    Open

  • 10

    STEP 1. DEFINE VARIABLES

    Open

  • 11

    STEP 2. FORMULATE THE CONSTRAINTS

    Open

  • 12

    STEP 3. FORMULATE THE OBJECTIVE FUNCTION

    Open

  • 13

    FULL VERSION OF THE LP PROBLEM FORMULATION

    Open

  • 14

    THE REDUCED VERSION

    Open

  • 1515

    GRAPHICAL SOLUTION

    Graphical solution shows that the optimum value of 8.1x1+10.8x2 is at:X1 = 26206 bbl/dayX2 = 6896 bbl/dayWith the maximum profit of 286758 $/day

    Open

  • 1616

    SIMPLEX METHOD (STANDARD MAXIMIZATION)

    Standard form of simplex maximization problem

    Maximize z = c1x1 + c2x2 + … + cnxn

    Subject to: a11x1 + a12x2 + … a1nxn ≤ b1

    … …

    am1x1 + am2x2 + … amnxn ≤ bm

    x1 ≥ 0, … xn ≥ 0

    Open

  • 1717

    SIMPLEX METHOD (STANDARD MAXIMIZATION)

    Steps in Simplex Method:1. If the problem is min z, convert it to max y = –z

    2. Introduceslack variables and convert the inequalities into equality constraints:ai1x1 + ai2x2 + … ainxn ≤ bi → ai1x1 + ai2x2 + … ainxn + si = bi

    if larger than and equal to, convert to less than and equal to, then introduce the slack variableai1x1 + ai2x2 + … ainxn ≥ bi → -ai1x1 - ai2x2 - … ainxn + si = -bi

    si ≥ 0

    3. Construct the problem into matrix of coefficients, vector of variables, and vector of the right handsideof the equations.

    4. Check if basic variables (variable that only appear in ONE (1) equation) are all positive. If not, these variables do not make feasible basic solution. Go to step 6.

    Open

  • 1818

    SIMPLEX METHOD (STANDARD MAXIMIZATION)

    5. Perform below calculations:a) Find pivot column based on the most negative coefficient of the objective functionb) Find pivot row, the smallest positive ratio between the righthandside numbers and the

    coefficients in the pivot column. The intersection between the pivot column and pivot row is the pivot point.

    c) Make the pivot point into 1d) Apply Gauss-Jordan elimination to make the rest of the numbers in the pivot column zero.e) Back to (a) until there is no negative coefficient

    6. Perform below calculations to remove all negative coefficients on the righthand side:a) Find pivot row based on the most negative coefficient on the righthand side numbersb) Find pivot column based on the most negative coefficient in the pivot row. The intersection

    between the pivot column and pivot row is the pivot point.c) Make the pivot point into 1d) Apply Gauss-Jordan elimination to make the rest of the numbers in the pivot column zero.e) Back to (a) until there is no negative coefficient

    Open

  • 1919Open

  • 20

    SIMPLE EXAMPLE

    A (0,4)

    B (0,1)

    C (1,0)

    D (16/7,9/7)

    E (1,2)

    x1-x2 ≤ 1

    3x1+4x2 ≤ 12

    x1+x2 ≥ 1

    x1

    x2

    Objective function, f = 2x1 + x2A(0,4), f = 4B(0,1), f = 1 → minimum valueC(1,0), f = 2D(16/7, 9/7), f = 41/7 → maximum valueE(1,2), f = 4

    Open

  • 21

    MAXIMIZATION

    Maximize f = 2x1 + x2Standardize the constraints: x1 + x2 ≥ 1 → -x1 - x2 ≤ -1 → -x1 - x2 +s1 = -13x1 + 4x2 ≤ 12 → 3x1 + 4x2 +s2 = 12x1 – x2 ≤ 1 → x1 – x2 + s3 = 1

    Make table in standard simplex LP maximization problem

    x1 x2 s1 s2 s3 f

    R1 -1 -1 1 0 0 0 -1

    R2 3 4 0 1 0 0 12

    R3 1 -1 0 0 1 0 1

    R4 -2 -1 0 0 0 1 0

    Check basic solution:x1 = 0 → not in feasible regionx2 = 0 → not in feasible regions1 = -1 → not feasibles2 = 12, s3 = 1 → OK (positive)

    Move to the feasible region by removing all negatives on the right-hand side

    Open

  • 22

    1ST ITERATION (MAXIMIZATION)

    x1 x2 s1 s2 s3 f

    R1 -1 -1 1 0 0 0 -1

    R2 3 4 0 1 0 0 12

    R3 1 -1 0 0 1 0 1

    R4 -2 -1 0 0 0 1 0

    A (0,4)

    B (0,1)

    C (1,0)

    D (16/7,9/7)

    E (1,2)

    x1-x2 ≤ 1

    3x1+4x2 ≤ 12

    x1+x2 ≥ 1

    x1

    x2

    Pick arbitrary between these two negatives

    1

    2

    Pivot selected is at step (3), which is -1Hence, R1 = R1/-1R2 = R2 -4R1R3 = R3 + R1R4 = R4 + R1

    3

    Open

  • 23

    1ST ITERATION (MAXIMIZATION)

    x1 x2 s1 s2 s3 f

    R1 1 1 -1 0 0 0 1

    R2 -1 0 4 1 0 0 8

    R3 2 0 -1 0 1 0 2

    R4 -1 0 -1 0 0 1 1

    Check basic solution:x1 = 0 → OKx2 = 1 → OKs1 = 0 → OKs2 = 8 → OKs3 = 2 → OK

    All are feasiblex1 and x2 are now at point B(0,1). Moved from previously (0,0)Continue with standard simplex, removing all negatives in R4

    A (0,4)

    B (0,1)

    C (1,0)

    D (16/7,9/7)

    E (1,2)

    x1-x2 ≤ 1

    3x1+4x2 ≤ 12

    x1+x2 ≥ 1

    x1

    x2

    Open

  • x1 x2 s1 s2 s3 f

    R1 1 1 -1 0 0 0 1

    R2 -1 0 4 1 0 0 8

    R3 2 0 -1 0 1 0 2

    R4 -1 0 -1 0 0 1 1

    24

    2ND ITERATION (MAXIMIZATION)

    A (0,4)

    B (0,1)

    C (1,0)

    D (16/7,9/7)

    E (1,2)

    x1-x2 ≤ 1

    3x1+4x2 ≤ 12

    x1+x2 ≥ 1

    x1

    x2

    Pick arbitrary between these two negatives

    2

    1

    Pivot selected is at step (3), which is 2Hence, R3 = R3/2R1 = R1 – R3R2 = R2 + R3R4 = R4 + R3

    3Both gives the same value, 1.Pick one

    Open

  • 25

    2ND ITERATION (MAXIMIZATION)

    x1 x2 s1 s2 s3 f

    R1 0 1 -1/2 0 -1/2 0 0

    R2 0 0 7/2 1 ½ 0 9

    R3 1 0 -1/2 0 ½ 0 1

    R4 0 0 -3/2 0 ½ 1 2

    Check basic solution:x1 = 1 → OKx2 = 0 → OKs1 = 0 → OKs2 = 9 → OKs3 = 0 → OK

    All are feasiblex1 and x2 are now at point C(1,0). Moved from previously B(0,1)Continue with standard simplex, removing all negatives in R4

    A (0,4)

    B (0,1)

    C (1,0)

    D (16/7,9/7)

    E (1,2)

    x1-x2 ≤ 1

    3x1+4x2 ≤ 12

    x1+x2 ≥ 1

    x1

    x2

    Open

  • x1 x2 s1 s2 s3 f

    R1 0 1 -1/2 0 -1/2 0 0

    R2 0 0 7/2 1 ½ 0 9

    R3 1 0 -1/2 0 ½ 0 1

    R4 0 0 -3/2 0 ½ 1 2

    26

    3RD ITERATION (MAXIMIZATION)

    A (0,4)

    B (0,1)

    C (1,0)

    D (16/7,9/7)

    E (1,2)

    x1-x2 ≤ 1

    3x1+4x2 ≤ 12

    x1+x2 ≥ 1

    x1

    x2

    The only negative

    2

    1

    Pivot selected is at step (3), which is 7/2Hence, R2 = R2/(7/2)R1 = R1 + 1/2R2R3 = R3 + 1/2R2R4 = R4 + 3/2R2

    3

    The only positive

    Open

  • 27

    3RD ITERATION (MAXIMIZATION)

    x1 x2 s1 s2 s3 f

    R1 0 1 0 1/7 -3/7 0 9/7

    R2 0 0 1 2/7 1/7 0 18/7

    R3 1 0 0 1/7 4/7 0 16/7

    R4 0 0 0 3/14 5/7 1 41/7

    Check basic solution:x1 = 16/7 → OKx2 = 9/7 → OKs1 = 18/7 → OKs2 = 0 → OKs3 = 0 → OK

    All are feasiblex1 and x2 are now at point D(16/7,9/7). Moved from previously C(0,1)Maximum value of f(16/7,9/7) = 41/7

    A (0,4)

    B (0,1)

    C (1,0)

    D (16/7,9/7)

    E (1,2)

    x1-x2 ≤ 1

    3x1+4x2 ≤ 12

    x1+x2 ≥ 1

    x1

    x2

    Open

  • 28

    MINIMIZATION

    Minimize f = 2x1 + x2 → transform to maximize, y = -f = - 2x1 - x2 Standardize the constraints: x1 + x2 ≥ 1 → -x1 - x2 ≤ -1 → -x1 - x2 +s1 = -13x1 + 4x2 ≤ 12 → 3x1 + 4x2 +s2 = 12x1 – x2 ≤ 1 → x1 – x2 + s3 = 1

    Make table in standard simplex LP maximization problem

    x1 x2 s1 s2 s3 y

    R1 -1 -1 1 0 0 0 -1

    R2 3 4 0 1 0 0 12

    R3 1 -1 0 0 1 0 1

    R4 2 1 0 0 0 1 0

    Check basic solution:x1 = 0 → not in feasible regionx2 = 0 → not in feasible regions1 = -1 → not feasibles2 = 12, s3 = 1 → OK (positive)

    Move to the feasible region by removing all negatives on the right-hand side

    Open

  • 29

    1ST ITERATION (MINIMIZATION)

    A (0,4)

    B (0,1)

    C (1,0)

    D (16/7,9/7)

    E (1,2)

    x1-x2 ≤ 1

    3x1+4x2 ≤ 12

    x1+x2 ≥ 1

    x1

    x2

    Pick arbitrary between these two negatives

    1

    2

    Pivot selected is at step (3), which is -1Hence, R1 = R1/-1R2 = R2 -4R1R3 = R3 + R1R4 = R4 - R1

    3x1 x2 s1 s2 s3 y

    R1 -1 -1 1 0 0 0 -1

    R2 3 4 0 1 0 0 12

    R3 1 -1 0 0 1 0 1

    R4 2 1 0 0 0 1 0

    Open

  • x1 x2 s1 s2 s3 y

    R1 1 1 -1 0 0 0 1

    R2 -1 0 4 1 0 0 8

    R3 2 0 -1 0 1 0 2

    R4 1 0 1 0 0 1 -1

    30

    1ST ITERATION (MINIMIZATION)

    A (0,4)

    B (0,1)

    C (1,0)

    D (16/7,9/7)

    E (1,2)

    x1-x2 ≤ 1

    3x1+4x2 ≤ 12

    x1+x2 ≥ 1

    x1

    x2

    Check basic solution:x1 = 0 → in feasible regionx2 = 1 → in feasible regions1 = 0 → feasibles2 = 8, s3 = 2 → OK (positive)

    All are feasibleX1 and x2 are now at B(1,0). Moved from (0,0)R4 are all positive. No further calculationMaximum value of y = -1 = -f Minimum value of f = -(-f) = 1

    Open

  • 31

    LET’S SOLVE THE REFINERY PROBLEM

    Step 1:0.8x1 + 0.44x2 ≤ 240000.05x1 + 0.1x2 ≤ 20000.1x1 + 0.36x2 ≤ 6000

    Step 2:0.8x1 + 0.44x2 + s1 = 24000 (a)0.05x1 + 0.1x2 + s2 = 2000 (b)0.1x1 + 0.36x2 + s3 = 6000 (c)f – 8.1x1 – 10.8x2 = 0

    Open

  • 32

    Make table in standard simplex LP maximization problem

    x1 x2 s1 s2 s3 f

    R1 0.8 0.44 1 0 0 0 24000

    R2 0.05 0.1 0 1 0 0 2000

    R3 0.1 0.36 0 0 1 0 6000

    R4 -8.1 -10.8 0 0 0 1 0

    Check basic solution:x1 = 0 → In feasible regionx2 = 0 → In feasible regions1, s2, s3 = 0 → feasible

    Non Basic Basic

    1ST ITERATION

    Open

  • 33

    x1 x2 s1 s2 s3 f

    R1 0.8 0.44 1 0 0 0 24000

    R2 0.05 0.1 0 1 0 0 2000

    R3 0.1 0.36 0 0 1 0 6000

    R4 -8.1 -10.8 0 0 0 1 0

    Gauss Jordan elimination:R1 = R1 – 0.44R3R2 = R2 - 0.1R3 R3 = R3/0.36R4 = R4 + 10.8R3

    2

    1

    Most negative column

    Smallest positive ratio

    Pivot point3

    Open

  • 34

    x1 x2 s1 s2 s3 f

    R1 61/90 0 1 0 -11/9 0 50000/3

    R2 1/45 0 0 1 -5/18 0 1000/3

    R3 5/18 1 0 0 25/9 0 50000/3

    R4 -5.1 0 0 0 0 1 180000

    Check solution:x1 = 0 → feasiblex2 = 50000/3 = 16666.67 → feasibles1, s2 ≥ 0 → feasibles3 = 0 → feasiblef = 180000 → point (1)

    Basic

    2ND ITERATION

    Open

  • 35

    x1 x2 s1 s2 s3 f

    R1 61/90 0 1 0 -11/9 0 50000/3

    R2 1/45 0 0 1 -5/18 0 1000/3

    R3 5/18 1 0 0 25/9 0 50000/3

    R4 -5.1 0 0 0 0 1 180000

    2

    1

    The only negative column

    Smallest positive ratio

    Pivot point3

    Gauss Jordan elimination:R1 = R1 – 61/90R2R2 = R2*45 R3 = R3 – 5/18R2R4 = R4 + 5.1R2

    Open

  • 36

    x1 x2 s1 s2 s3 f

    R1 0 0 1 -30.5 7.25 0 6500

    R2 1 0 0 45 -12.5 0 15000

    R3 0 1 0 -12.5 6.25 0 12500

    R4 0 0 0 229.5 -33.75 1 256500

    Check solution:x1 = 15000 → feasiblex2 = 12500 → feasibles1 = 0 → feasibles2, s3 ≥ 0 → feasiblef = 256500 → point (2)

    Basic

    3RD ITERATION

    Open

  • 37

    x1 x2 s1 s2 s3 f

    R1 0 0 1 -30.5 7.25 0 6500

    R2 1 0 0 45 -12.5 0 15000

    R3 0 1 0 -12.5 6.25 0 12500

    R4 0 0 0 229.5 -33.75 1 256500

    2

    1

    The only negative column

    Smallest positive ratio

    Pivot point3

    Gauss Jordan elimination:R1 = R1/7.25R2 = R2 + 12.5R1 R3 = R3 – 6.25R1R4 = R4 + 33.75R1

    Open

  • 38

    x1 x2 s1 s2 s3 f

    R1 0 0 4/29 -4.21 1 0 26000/29

    R2 1 0 50/29 2830/9 0 0 26206

    R3 0 1 -0.86 -38.8 0 0 6896

    R4 0 0 4.65 87.41 0 1 286758

    Check solution:x1 = 26206 → feasiblex2 = 6896→ feasibles1, s3 = 0 → feasibles2 ≥ 0 → feasiblef = 286758 → point (3)No more negative values in R4. Iteration stops

    Basic

    4TH ITERATION

    Basic

    Open

  • 39

    x1 x2 s1 s2 s3 f

    R1 0 0 4/29 -4.21 1 0 26000/29

    R2 1 0 50/29 2830/9 0 0 26206

    R3 0 1 -0.86 -38.8 0 0 6896

    R4 0 0 4.65 87.41 0 1 286758

    Basic

    4TH ITERATION

    Basic

    Maximum value is 286758 $/dayx1 = 26206 bbl/dayx2 = 6896 bbl/day

    Open

  • 40

    EXCEL SOLVER

    We’ll do the same exercise in Excel Solver

    Open

  • 41

    SENSITIVITY ANALYSIS

    • In all LP problems, all coefficients are supplied as input data to the model

    • These coefficients are not 100% certain. There are uncontrollable situations

    • Hence, only finding the optimal solution does not solve a practical problem

    • Thus, sensitivity analysis is done by varying the coefficients and check theresults

    Open

  • 42

    SENSITIVITY ANALYSIS FOR SMALL PROBLEM

    This final table from the refinery case, has the following equation:f = -4.65s1 – 87.41s2 + 286758

    See it in a different perspective:At s1 and s2 = 0, we get the maximum value of f, which is 286758

    x1 x2 s1 s2 s3 y

    R1 0 0 4/29 -4.21 1 0 26000/29

    R2 1 0 50/29 2830/9 0 0 26206

    R3 0 1 -0.86 -38.8 0 0 6896

    R4 0 0 4.65 87.41 0 1 286758

    Open

  • 43

    SENSITIVITY ANALYSIS FOR SMALL PROBLEM

    In the optimal solution (point (3)), both gasoline and kerosene are constrained. But not fuel oil!

    (Example) constraint for gasoline: 0.8x1 + 0.44x2 ≤ 24000, x1 and x2 are the amount of crude 1 and crude 2 (bbl/day), or0.8x1 + 0.44x2 + s1 = 24000 → s1 (slack for gasoline produced) is 0 in the optimal solution

    If we relax the production of gasoline by 1 unit (s1 = -1 bbl/day), then Δf = 4.65 $/day.This 4.65$/bbl is the marginal price for constraint A (gasoline).

    A = constraint for gasolineB = constraint for keroseneC = constraint for fuel oil

    Equation from the final table:f = -4.65s1 – 87.41s2 + 286758

    Open

  • 44

    SENSITIVITY ANALYSIS

    • Similarly, we can do the same thing with the kerosene constraint. Its marginal price is 87.41 $/bbl.

    • Based on the final equation (f = -4.65s1 – 87.41s2 + 286758), small change in fuel oil does not make any difference.

    • If crude oil price change, the coefficients in the objective function will change.

    • In the end, iterative calculations are necessary!

    Open

  • 45

    DEGENERATE LP PROBLEMS

    Degenerate LP problems are LP problems that:- does not have a feasible region, or- does not have a finite solution

    Minimize f(x) = -x1-x2Subject to: 3x1-x2 ≥ 0 (A)

    x2 ≤ 3 (B)x1, x2 ≥ 0

    Minimize f(x) = -x1-x2Subject to: x1+x2 ≤ -2 (A)

    x1 +2x2 ≤ 0 (B)x1, x2 ≥ 0

    The bigger the number, the minimum the objective function → has no finite solution

    Open

  • 46

    DUALITY IN LINEAR PROGRAMMING

    • Marginal prices of:• gasoline = $ 4.65/bbl• kerosene = $ 87.41/bbl, while • fuel oil = $ 0/bbl

    • If maximum capacity of these products are multiplied by their marginal prices, we get

    4.65(24000) + 87.41(2000) + 0(6000) = 286758

    This is the same as the optimum profit calculated for this problem

    • This equivalence is an important property of LP, known as “duality”

    • It implies that original LP (called “primal” problem) could be formulated in an alternative way called “dual” problem

    Open

  • 47

    DUAL PROBLEM FORMULATION

    Open

  • 48

    SIMPLEX METHOD

    (MINIMIZATION VIA DUAL PROBLEM)

    Open

  • 49

    SIMPLEX METHOD

    (MINIMIZATION VIA DUAL PROBLEM)

    Open

  • Original problem:

    Minimize f = 3x1 + 5x2 f = cTx

    Subject to x1 + 3x2 ≥ 10 Ax ≥ b

    2x1 – x2 ≥ 4

    -x1 + 4x2 ≥ -2

    -x1 – x2 ≥ -20

    x1, x2 ≥ 0

    Dual problem: f = bTy

    ATy ≤ c

    Maximize f = 10y1 + 4y2 – 2y3 – 20y4y1 + 2y2 – y3 – y4 ≤ 1

    3y1 – y2 + 4y3 – y4 ≤ 5

    • Dual problem is advised for problems with many constraints and few variables.

    • Minimization problems are solved by converting them to the maximization problem via dual problem.

    50

    EXAMPLE

    Open

  • ▪ Please minimize w = 29y1 + 10y2▪ Subject to: 3y1 + 2y2 ≥ 2

    5y1 + y2 ≥ 3

    y1, y2 ≥ 0

    51

    PAIR TEST: DUALITY PROBLEM

    Open

  • ▪ Standard linear programming problem:

    • Maximization

    • Inequality is less than or equal to (≤)

    ▪ Non-standard linear programming problem:

    • Minimization

    • Inequality is combination of both ≤ and ≥

    ▪ How to solve non-standard linear programming problem:

    • Transform into standard maximization problem

    • Change minimize to maximize

    • Change inequality from ≥ to ≤

    • If some of the constraints are substituted into the other constraints and the objective function, make sure that the respective variables have to be positive (all variables are positive) by adding necessary additional constraints

    • Use dual problem, if applicable

    • JUST USE MS EXCEL or any other LP software! ☺

    52

    NON-STANDARD LINEAR PROGRAMMING PROBLEM

    Open

  • ▪ Your company just bought two lubricant factories as subsidiary companies.Until now, they are only selling the lubricants via historical partnershipwith their customers. Apparently, they have two same customers.

    ▪ This situation does not make the new supply chain manager happy. So, hecalls you as the recommended senior process engineer within the company.

    ▪ He tells you that the 1st factory has 400 tons of lubricants in their storage,while the other has 300 tons. The 1st customer needs 200 tons oflubricants, while the other requires 300 tons. The supply chain managershows you the cost of shipments ($/ton) as shown below.

    ▪ Then, he asks for your advice on how much lubricant from each factoryshould be sent to each customer. What are you going to say?

    53

    FINAL QUESTION: CASE STUDY

    Open

  • 54

    Objective and Constraints formulation

    Multi variable

    One variable

    Unconstrained optimization

    Constrained Optimization

    Methods:• Function value,

    • Bracketing,• Newton,• Secant

    Methods:• Simplex,• Newton,• Steepest

    descentLagrange multiplier

    and Karush Kuhn Tucker algorithm

    Linear programming via Simplex method

    Non Linear programming

    Methods:• SQP,• GRG,

    • PenaltyInteger programming via Branch and Bound

    COURSE OVERVIEW

    Open