ILOG CPLEX 11.0 User's Manual > Discrete Optimization > Solving Mixed Integer Programming Problems (MIP) > Troubleshooting MIP Performance Problems > Trouble Finding More than One Feasible Solution

Trouble Finding More than One Feasible Solution

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For some models, ILOG CPLEX finds an integer feasible solution early in the process and then does not find a better one for quite a while. One possibility, of course, is that the first feasible solution is optimal and will eventually be proven optimal. In that case, there are no better solutions.

One possible approach to finding more feasible solutions is to increase the frequency of the node heuristic, by setting the heuristic frequency parameter (HeurFreq, CPX_PARAM_HEURFREQ) to a value such as 10 or 5 or even 1. This heuristic can be expensive, so exercise caution when setting this parameter to values less than 10.

Another approach to finding more feasible solutions is to try a node selection strategy alternative. Setting the node selection parameter (NodeSel , CPX_PARAM_NODESEL) to 2 invokes a best-estimate search, which sometimes does a better job of locating good quality feasible solutions than the default node selection strategy.

The settings 1 (one) and 4 of the MIP emphasis parameter (MIPEmphasis, CPX_PARAM_MIPEMPHASIS) both address the issue of finding feasible solutions. These parameter settings are also worth considering for this symptom of difficulty finding more than one feasible solution.

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