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Operations Research Models and Methods
Computation Section
Mathematical Programming Model Builder

The Mathematical Programming Model Builder add-in builds models for linear and integer programming. They can be solved by either the Excel Solver add-in or the Jensen LP/IP solver that is part of this collection. The add-in provides four different model formats that are described in the pages of this section. One of these formats is similar to the model created by the Linear/Integer command of the Math Programming add-in. The Math Programming add-in has so many features that it has grown very large in memory requirements. Since the MP Model Builder add-in is limited to only LP and IP forms, it is much smaller than the Math Programming add-in. It also has new features that may be useful.

Two of the new formats use lists rather than matrices to store the constraint coefficients. For cases with sparse coefficient matrices (many zeros and only a few non-zero entries), storing the list of nonzero coefficients is more efficient than storing the matrix. Another justification for the list model is the difficulty of constructing and correcting a matrix model that has more than just a few rows and columns. I envision creating an add-in that builds models for specific problem categories. This automatic model construction will be simpler with list formats.

When the MP Model Builder add-in installed, the new control commands are placed on the ORMM menu. Note that the LP/IP Solver is also installed. That program is used to solve the models for this section. The Excel Solver can also be used to obtain solutions.

math programming dialog

The principal command on the menu is Linear/Integer. All models begin with this command as illustrated on the next page.

A model worksheet includes buttons that change the model or call the solution algorithms. An error dialog concerning missing links will be presented when a file is opened on a computer different than the computer that created the model. It is best to cancel this dialog. Then choose the Add Buttons command to replace all the buttons on math programming models in the workbook. Before saving a workbook that will be transferred to another computer, choose the Remove Buttons command. This removes all the buttons in the workbook so a link message does not appear when the model is opened on a different computer. The buttons can subsequently be added with the Add Buttons command. The demonstration workbook for this add-in has its buttons removed, so the first thing to do is to select the add buttons command.

To solve models, one of the solver add-ins must be installed. The MP Model Builder add-in builds models, but it does not solve them. The solver add-ins can solve models, but cannot build them. For these examples we have installed the LP/IP Solver add-in. Be sure to use the latest version of the add-in.


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Operations Research Models and Methods
by Paul A. Jensen
Copyright 2004 - All rights reserved

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