Stopping Criteria for the Populate Procedure

ILOG CPLEX 11.0 User's Manual > Discrete Optimization > Solution Pool: Generating and Keeping Multiple Solutions > Populating the Solution Pool > Stopping Criteria for the Populate Procedure

Stopping Criteria for the Populate Procedure

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Optimality is not a stopping criterion for the populate procedure. Even if the optimality gap is zero, this procedure will still try to find alternative solutions. The stopping criteria for populating the solution pool are these:

Populate limit. This parameter controls how many solutions are generated before the populate procedure stops. Its default value is 20. Consequently, the procedure stopped after generating 20 solutions in the example with model location.lp in Example: Calling Populate.

PopulateLim in Concert Technology
CPX_PARAM_POPULATELIM in the Callable Library (C API)
mip limits populate in the Interactive Optimizer

The parameter to limit the number of integer solutions in a MIP (IntSolLim in Concert Technology or CPX_PARAM_INTSOLLIM in the Callable Library or mip limits solutions in the Interactive Optimizer) does not apply to the populate procedure; if you want to limit the populate procedure, apply the populate limit parameter (PopulateLim, CPX_PARAM_POPULATELIM) instead.

Time limit, as in a standard MIP optimization.

TiLim in Concert Technology
CPX_PARAM_TILIM in the Callable Library (C API)
timelimit in the Interactive Optimizer

Node limit, as in a standard MIP optimization.

NodeLim in Concert Technology
CPX_PARAM_NODELIM in the Callable Library (C API)
mip limit nodes in the Interactive Optimizer

In the absence of other stopping criteria, the populate procedure stops when it cannot enumerate any more solutions.

In particular, if you specify an objective tolerance with the relative or absolute solution pool gap parameters, populate stops if it cannot enumerate any more solutions within the specified objective tolerance.

However, there may exist additional solutions that are feasible, and if you have specified an objective tolerance, those feasible solutions may also satisfy this additional criterion. (For example, there may be a great many solutions to a given problem with the same integer values but different values for continuous variables.) Depending on the solution pool intensity parameter, populate may or may not enumerate all possible solutions. Consequently, populate may stop when it has enumerated only a subset of the solutions satisfying your criteria.

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