Download presentation

Presentation is loading. Please wait.

Published byMarco Tolley Modified over 2 years ago

1
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

4 Linear Programming: An Algebraic Approach The Simplex Method with Standard Maximization Problems Standard Minimization Problems Nonstandard Problems Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

2
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

The Simplex Method The simplex method is an iterative process. Starting at some initial feasible solution (a corner point – usually the origin), each iteration moves to another corner point with an improved (or at least not worse) value of the objective function. Iteration stops when an optimal solution (if it exists) is found. Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

3
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

A Standard (maximization) Linear Programming Problem: The objective function is to be maximized. All the variables involved in the problem are nonnegative. Each constraint may be written so that the expression with the variables is less than or equal to a nonnegative constant. Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

4
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

Ex. A standard maximization problem: Maximize P = 4x + 5y Subject to First introduce nonnegative slack variables to make equations out of the inequalities: Next, rewrite the objective function Set = 0 with a 1 on P: –4x – 5y + P = 0 Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

5
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

Form the system: Basic variables Write as a tableau: Nonbasic variables Variables in non-unit columns are given a value of zero, so initially x = y = 0. Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

6
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

Choose a pivot: Ratios: Select column: select most negative entry in the last row (to left of vertical line). Select row: select smallest ratio: constant/entry (using only entries from selected column) Next using the pivot, create a unit column Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

7
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

8
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

Ratios: Repeat steps Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

9
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

All entries in the last row are nonnegative therefore an optimal solution has been reached: Assign 0 to variables w/out unit columns (u, v). Notice x = 1, y = 5, and P = 25 (the max). Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

10
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

The Simplex Method: Set up the initial simplex tableau. If all entries in the last row are nonnegative then an optimal solution has been reached, go to step 4. Perform the pivot operation: convert pivot to a 1, then use row operations to make a unit column. Return to step 2. Determine the optimal solution(s). The value of the variable heading each unit column is given by the corresponding value in the column of constants. Variables heading the non-unit columns have value zero. Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

11
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

Multiple Solutions There are infinitely many solutions if and only if the last row to the right of the vertical line of the final simplex tableau has a zero in a non-unit column. No Solution A linear programming problem will have no solution if the simplex method breaks down (ex. if at some stage there are no nonnegative ratios for computation). Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

12
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

Minimization with Constraints Ex. Minimize C = –4 x – 5y Subject to Notice if we let P = –C = 4x + 5y we have a standard maximization problem. If we solve this associated problem we find P = 25, therefore the minimum is C = –25. Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

13
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

A Standard (minimization) Linear Programming Problem: The objective function is to be minimized. All the variables involved in the problem are nonnegative. Each constraint may be written so that the expression with the variables is greater than or equal to a nonnegative constant. Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

14
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

The Dual Problem Maximization problems can be associated with minimization problems (and vice versa). The original problem is called the Primal and the associated problem is called the Dual. Theorem of Duality A primal problem has a solution if and only if the dual has a solution. Both objective functions attain the same optimal value. The optimal solution of the primal appears under the slack variables in the last row of the final simplex tableau associated with the dual. Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

15
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

Ex. Minimize C = 10x + 11y Subject to Write down the primal information: Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

16
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

Interchange the columns and rows and use variables u, v, w. This can be represented by the problem: Maximize P = 300u + 300v + 250w Subject to This is a standard maximization problem Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

17
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

Create the initial simplex tableau adding slack variables x and y. pivot Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

18
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

19
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

20
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

This is the final tableau with x = 15, y = 5, and P = C = 205. Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

21
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

Ex. A nonstandard maximization problem: Maximize P = 8x + 3y Subject to First change the inequalities to less than or equal to. Now proceed with the simplex method Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

22
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

Introduce slack variables to make equations out of the inequalities and set the objective function = 0: The initial tableau and notice v = –2 (not feasible): We need to pivot to a feasible solution Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

23
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

Ratios 8 2 Locate any negative number in the constant column ( –2). Now go to the first negative to the left of that constant (–1). This determines the pivot column. The pivot row is found by examining the positive ratios. So –1 is our pivot. Create unit column Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

24
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

New pivot since it is the only positive ratio Note: now we have a feasible solution proceed with simplex Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

25
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

This is the final tableau: x = 2, y = 4, P = 28 Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

26
**Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc**

The Simplex Method for Nonstandard Problems If necessary, rewrite as a maximization problem. If necessary, rewrite inequalities as less or equal to. Introduce slack variables and write simplex tableau. If no negative constants (upper column) use simplex method, otherwise go to step 5. Pick a negative entry in a row with a negative constant (this is the pivot column). Compute positive ratios to determine pivot row. Then pivot and return to step 4. Copyright (c) 2003 Brooks/Cole, a division of Thomson Learning, Inc

Similar presentations

OK

Minimization Problem First Approach Introduce the basis variable To solve minimization problem we simple reverse the rule that is we select the.

Minimization Problem First Approach Introduce the basis variable To solve minimization problem we simple reverse the rule that is we select the.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt online viewer free Ppt on different types of trees Ppt on content development services Ppt on statistics in maths what does the range Ppt on japanese tea ceremony Ppt online open port Ppt on central administrative tribunal bench Moral stories for kids ppt on batteries Ppt on adr and gdr group Ppt on new zealand culture for kids