MPL for Windows Manual
MPL for Windows Manual
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You can change the preprocessing options for XPRESS by choosing XPRESS parameters from the Options menu and then pressing the Preprocessing tab. This will display the preprocessing options for XPRESS in the dialog box as shown below:
Figure 4.54: The Preprocessing Tab in XPRESS Options Dialog Box
The presolve facility can greatly improve performance by modifying the user's matrix so that it is easier to solve. The presolve algorithms identify and remove redundant rows and columns, thus reducing the size of the matrix. If the model contains global entities, integer presolve methods such as bound fixing and coefficient tightening are also applied to tighten the LP relaxation.
When a solution to a presolved problem has been found it is internally postsolved so that the user can access a solution to the original problem.
If Use presolve is On, the optimizer will begin by preprocessing the matrix. This reduces the active matrix size by identifying redundant rows and columns by inspection and modifying the matrix in order to make it easier to optimize.
Control of the infeasibility diagnosis during presolve. If On, the logical deductions made by presolve to deduce infeasibility will be displayed.
Reduced cost fixing at each node. Default is On.
Logical preprocessing at each node. Default is On.
Probing set at the top node. Default is On.
If any of these three above options are selected, integer preprocessing for MIP problems will be performed at each node of the branch-and-bound search tree (including the top node). If a variable is fixed at a node, it remains fixed at all its child nodes but it is not deleted from the matrix (unlike the variables fixed by presolve).