ILOG CPLEX 11.0 User's Manual

improve the solution pool. Changes that have an impact on the solutions that populategenerates and stores include these:◆◆◆changing parameter settings;adding filters;removing filters;◆ changing characteristics of filters.Changes of the model itself, such as altering the objective function, are treated differently.For details, see Model Changes and the Solution Pool on page 315.Persistence of Solutions in the Solution PoolSuccessive calls to MIP optimization or populate create solutions that are stored in thesolution pool. However, each call to MIP optimization or populate applies only to the subsetof solutions created in the current call; the call does not affect the solutions already in thepool, as long as the model has not changed. In other words, solutions in the pool persistthrough successive calls on the same model.Model Changes and the Solution PoolWhen a user modifies a model, for example, by adding constraints or changing thecoefficients of the objective function, the existing solutions already in the solution pool mayor may not be feasible in terms of the changed model. Therefore, immediately after changinga model, the user cannot access the solution pool. In fact, if the user attempts to query thesolution pool after changing a model, the solution pool query routines and methods return anerror: CPXERR_NO_SOLNPOOL.However, the solutions in the solution pool still exist and are available as MIP starts,accessible through these methods and routines:◆◆◆IloCplex::writeMIPStart in the C++ API;IloCplex.writeMIPStart in the Java API;Cplex.WriteMIPStart in the .NET API;◆ CPXgetsolnpoolmipstart and CPXmstwritesolnpool in the Callable Library (CAPI).Moreover, if the advanced start parameter (AdvInd, CPX_PARAM_ADVIND) is set to a valuegreater than zero, then after the user changes a model, the next call to MIP optimization orpopulate will try to re-use the existing solutions to derive solutions for the newly changedmodel.ILOG CPLEX 11.0 — USER’ S MANUAL 315