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params_c.c
/* Copyright 2023, 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;
}
