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params_c.c
/* Copyright 2019, Gurobi Optimization, LLC */ /* Use parameters that are associated with a model. A MIP is solved for a few seconds with different sets of parameters. The one with the smallest MIP gap is selected, and the optimization is resumed until the optimal solution is found. */ #include <stdlib.h> #include <stdio.h> #include <math.h> #include "gurobi_c.h" int main(int argc, char *argv[]) { GRBenv *env = NULL, *modelenv = NULL, *bestenv = NULL; GRBmodel *model = NULL, *bestmodel = NULL; int error = 0; int ismip, i, mipfocus; double bestgap, gap; if (argc < 2) { fprintf(stderr, "Usage: params_c filename\n"); exit(1); } error = GRBloadenv(&env, "params.log"); if (error) goto QUIT; /* Read model and verify that it is a MIP */ error = GRBreadmodel(env, argv[1], &model); if (error) goto QUIT; error = GRBgetintattr(model, "IsMIP", &ismip); if (error) goto QUIT; if (ismip == 0) { printf("The model is not an integer program\n"); exit(1); } /* Set a 2 second time limit */ modelenv = GRBgetenv(model); if (!modelenv) { printf("Cannot retrieve model environment\n"); exit(1); } error = GRBsetdblparam(modelenv, "TimeLimit", 2); if (error) goto QUIT; /* Now solve the model with different values of MIPFocus */ bestmodel = GRBcopymodel(model); if (!bestmodel) { printf("Cannot copy model\n"); exit(1); } error = GRBoptimize(bestmodel); if (error) goto QUIT; error = GRBgetdblattr(bestmodel, "MIPGap", &bestgap); if (error) goto QUIT; for (i = 1; i <= 3; ++i) { error = GRBreset(model, 0); if (error) goto QUIT; modelenv = GRBgetenv(model); if (!modelenv) { printf("Cannot retrieve model environment\n"); exit(1); } error = GRBsetintparam(modelenv, "MIPFocus", i); if (error) goto QUIT; error = GRBoptimize(model); if (error) goto QUIT; error = GRBgetdblattr(model, "MIPGap", &gap); if (error) goto QUIT; if (bestgap > gap) { GRBmodel *tmp = bestmodel; bestmodel = model; model = tmp; bestgap = gap; } } /* Finally, free the extra model, reset the time limit and continue to solve the best model to optimality */ GRBfreemodel(model); bestenv = GRBgetenv(bestmodel); if (!bestenv) { printf("Cannot retrieve best model environment\n"); exit(1); } error = GRBsetdblparam(bestenv, "TimeLimit", GRB_INFINITY); if (error) goto QUIT; error = GRBoptimize(bestmodel); if (error) goto QUIT; error = GRBgetintparam(bestenv, "MIPFocus", &mipfocus); if (error) goto QUIT; printf("Solved with MIPFocus: %i\n", mipfocus); QUIT: /* Error reporting */ if (error) { printf("ERROR: %s\n", GRBgeterrormsg(env)); exit(1); } /* Free best model */ GRBfreemodel(bestmodel); /* Free environment */ GRBfreeenv(env); return 0; }