Exam 18: Simplex-Based Sensitivity Analysis and Duality

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For this optimal simplex tableau, the right-hand sides for the two original ≥\ge constraints were 300 and 250. The problem was a minimization. Basis -100 -110 -95 0 0 -95 0 -1.5 1 1 -1.5 75 -100 1 2 0 -1 1 50 -100 -57.5 -95 5 42.5 -12125 - 0 -52.5 0 -5 -42.5 a.What would the new solution be if the right-hand side value in the first constraint had been 325? b.What would the new solution be if the right-hand side value for the second constraint had been 220?

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a.x3 = 50, x1 = 75, Z = 12250
b.x3 = 30, x1 = 80, Z = 10850

The ranges for which the right-hand side values are valid are the same as the ranges over which the dual prices are valid.

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The range of optimality for a basic variable defines the objective function coefficient values for which the variable will remain part of the current optimal basic feasible solution.

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Given the following linear programming problem Max 10x1 + 12x2 s.t. 1x1 + 2x2 ≥\ge 40 5x1 + 8x2 ≤\le 160 1x1 + 1x2 ≤\le 40 x1, x2 ≥\ge 0 the final tableau is Basis 10 12 0 0 0 12 0 1 -2.5 -.5 0 20 10 1 0 4 1 0 0 0 0 0 -1.5 -5 1 20 10 12 10 4 0 240 - 0 0 -10 -4 0 a.Find the range of optimality for c1 and c2. b.Find the range of feasibility for b1, b2, and b3. c.Find the dual prices.

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The range of feasibility indicates right-hand side values for which

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The linear programming problem Max 6x1 + 2x2 + 3x3 + 4x4 s.t. x1 + x2 + x3 + x4 ≤\le 100 4x1 + x2 + x3 + x4 ≤\le 160 3x1 + x2 + 2x3 + 3x4 ≤\le 240 x1, x2, x 3, x4 ≥\ge 0 has the final tableau Basis 6 2 3 4 0 0 0 2 0 1 1/2 0 3/2 0 -1/2 30 6 1 0 0 0 -1/3 1/3 0 20 4 0 0 1/2 1 -1/6 -1/3 1/2 50 6 2 3 4 2.33 .67 1 380 - 0 0 0 0 -2.33 -.67 -1 Fill in the table below to show what you would have found if you had used The Management Scientist to solve this problem. LINEAR PROGRAMMING PROBLEM MAX 6X1+2X2+3X3+4X4 S.T. 1) 1X1 + 1X2 + 1X3 + 1X4 < 100 2) 4X1 + 1X2 + 1X3 + 1X4 < 160 3) 3X1 + 1X2 + 2X3 + 3X4 < 240 OPTIMAL SOLUTION Objective Function Value == Variable Value Reduced Cost X1 - - X2 - - X3 - - X4 - - Constraint Slack/Surplus Dual Price 1 - - 2 - - 3 - -  OBJECTIVE COEFFICIENT RANGES \text { OBJECTIVE COEFFICIENT RANGES } Variable Lower Limit Current Value Upper Limit 1 - - - 2 - - - 3 - - - 4 - - -  RIGHT HAND SIDE RANGES \text { RIGHT HAND SIDE RANGES } Constraint Lower Limit Current Value Upper Limit 1 - - - 2 - - - 3 - - -

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Write the dual of the following problem Min Z = 2x1 -3x2 + 5x3 s.t. -3x1 + 2x2 + 5x3 ≥\ge 7 2x1 -x3 ≥\ge 5 4x 2 + 3x3 ≥\ge 8.

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The range of optimality is calculated by considering changes in the cj - zj value of the variable in question.

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Explain the simplex tableau location of the dual constraint for each type of constraint.

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If the dual price for b1 is 2.7, the range of feasibility is 20 ≤\le b1 ≤\le 50, and the original value of b1 was 30, which of the following is true?

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If the simplex tableau is from a maximization converted from a minimization, the signs and directions of the inequalities that give the objective function ranges will need to be adjusted to apply to the original coefficients.

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When sensitivity calculations yield several potential upper bounds and several lower bounds, how is the range determined?

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A linear programming problem with the objective function 3x1 + 8x2 has the optimal solution x1 = 5, x2 = 6. If c2 decreases by 2 and the range of optimality shows 5 ≤\le c2 ≤\le 12, the value of Z

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For the following linear programming problem Max Z -2x1 + x2 - x3 s.t. 2x1 + x2 ≤\le 7 1x1 + x2 + x3 ≥\ge 4 the final tableau is Basis -2 1 -1 0 0 - 0 1 0 -1 1 1 -1 3 1 2 1 0 1 0 0 7 2 1 0 1 0 0 7 - -4 0 1 -1 0 - a.Find the range of optimality for c1, c2 , c3.c4, c5 , and c6. b.Find the range of feasibility for b1, and b2.

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The dual variable represents

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Dual prices and ranges for objective function coefficients and right-hand side values are found by considering

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The entries in the associated slack column of the final tableau indicate the changes in the values of the current basic variables corresponding to a one-unit increase in the right-hand side.

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The primal problem is Min 2x1 + 5x2 + 4x3 s.t. x1 + 3x2 + 3x3 ≥\ge 30 3x1 + 7x2 + 5x3 ≥\ge 70 x1, x2, x3 ≥\ge 0 The final tableau for its dual problem is Basis 30 70 0 0 0 70 0 1 3/4 0 -1/4 1/2 0 0 0 -3/2 1 -1/2 0 30 1 0 -5/4 0 3/4 1/2 30 70 15 0 5 50 - 0 0 -15 0 -5 Give the complete solution to the primal problem.

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For an objective function coefficient change outside the range of optimality, explain how to calculate the new optimal solution. Must you return to the (revised) initial tableau?

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The improvement in the value of the optimal solution per-unit increase in a constraint's right-hand side is

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