Example: Few or Many Solutions through Intensity Parameter

ILOG CPLEX 11.0 User's Manual > Discrete Optimization > Solution Pool: Generating and Keeping Multiple Solutions > Parameters of the Solution Pool > Example: Few or Many Solutions through Intensity Parameter

Example: Few or Many Solutions through Intensity Parameter

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Use the solution pool intensity parameter (SolnPoolIntensity, CPX_PARAM_SOLNPOOLINTENSITY) to balance the number of solutions generated and the amount of time or memory consumed. Lower intensity values generate fewer solutions, whereas higher intensity values generate more solutions.

If you need many solutions, but do not want to impair performance too greatly, the value 2 (moderate) is a good choice for most models.

For example, the following session in the Interactive Optimizer reads a model in LP format of the Example: Simple Facility Location Problem.The session then effectively removes the stopping criterion of the populate limit parameter by setting it very high.

read location.lp
set mip limits populate 10000
set mip pool intensity 2
set mip pool relgap 0.1
populate

You can see from the log that setting the pool intensity to 2 yields results faster than when populate is called after MIP optimization at the default value of solution pool intensity.

If you set the solution pool intensity parameter to 3 (aggressive) or 4 (very aggressive), then an even larger number of solutions will be produced.

At solution pool intensity 2, a large number of solutions are produced (in this case, 196 solutions, though the precise number of solutions may vary on your platform).

If you set solution pool intensity at 3 instead, populate will generate a greater number of solutions (in this case, 208 solutions).

Likewise, if you set solution pool intensity at 4 instead, a very great number of solutions will be produced and stored in the solution pool, as this setting exhaustively enumerates solutions.

In this small example, the settings 3 and 4 happen to produce the same number of solutions (208), but in general it will not be the case that the two settings have the same effect.

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