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Modeling and Solving Lp Problems in a Spreadsheet

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Modeling and Solving LP Problems in a Spreadsheet
Chapter 3

C.T. Ragsdale. 2008. Spreadsheet Modeling & Decision Analysis, 5th E. Revised, Thompson
1

Section 1

EXCEL SOLVER

2

Introduction
• Solving LP problems graphically is only possible when there are two decision variables • Few real-world LP have only two decision variables • Fortunately, we can now use spreadsheets to solve LP problems

3

LP Solvers
• Conventional
– MPS (IBM) – LINDO, GINO – GAMS – AMPL

• Algebraic Language • Spreadsheet Modeling

• The company that makes the Solver in Excel, Lotus 12-3, and Quattro Pro is Frontline Systems, Inc.
Check out their web site: http://www.solver.com

– Frontline Solver, Premium Solver, Risk Solver – What’s Best?

4

Steps in Implementing an LP Model in a Spreadsheet
1. Organize the data for the model on the spreadsheet. 2. Reserve separate cells in the spreadsheet for each decision variable in the model. 3. Create a formula in a cell in the spreadsheet that corresponds to the objective function. 4. For each constraint, create a formula in a separate cell in the spreadsheet that corresponds to the left-hand side (LHS) of the constraint.

5

The Simple Farm Model Again! max π = x1 + 1.5x2 s/t x1 + 2x2 ≤ 160 3x1 + 2x2 ≤ 240 x1 ≥ 0, x2 ≥ 0

6

Implementing the Model

See file FarmEx original.xls
7

Cell Labels

8

How Solver Views the Model
• Target cell - the cell in the spreadsheet that represents the objective function • Changing cells - the cells in the spreadsheet representing the decision variables • Constraint cells - the cells in the spreadsheet representing the LHS formulas on the constraints

9

Let’s go back to Excel and see how Solver works...

10

11

Solver Dialog

Standard Solver vs. Premium Solver
12

Solver Option

13

Answer Report
Microsoft Excel 10.0 Answer Report

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