mip2_c.c
/*版权所有2023,Gurobi O狗万app足彩ptimization, LLC */ /*本例从文件中读取一个MIP模型，求解它，并打印求解MIP时生成的所有可行解的客观值。然后它创建固定模型并求解该模型。*/ #include #include #include #include "gurobi_c.h" int main(int argc, char *argv[]) {GRBenv *env = NULL;GRBmodel *model = NULL;GRBmodel *fixed = NULL;Int错误= 0;int ismip;Int j, k, solcount, numvars;双objn;Int optimstatus, foptimstatus; double objval, fobjval; char *varname; double x; /* To change settings for a loaded model, we need to get the model environment, which will be freed when the model is freed. */ GRBenv *menv, *fenv; if (argc < 2) { fprintf(stderr, "Usage: mip2_c filename\n"); exit(1); } /* Create environment */ error = GRBloadenv(&env, "mip2.log"); if (error) goto QUIT; /* Read model from file */ error = GRBreadmodel(env, argv[1], &model); if (error) goto QUIT; error = GRBgetintattr(model, "IsMIP", &ismip); if (error) goto QUIT; if (ismip == 0) { printf("Model is not a MIP\n"); goto QUIT; } /* Get model environment */ menv = GRBgetenv(model); if (!menv) { fprintf(stderr, "Error: could not get model environment\n"); goto QUIT; } /* Solve model */ error = GRBoptimize(model); if (error) goto QUIT; /* Capture solution information */ error = GRBgetintattr(model, GRB_INT_ATTR_STATUS, &optimstatus); if (error) goto QUIT; printf("\nOptimization complete\n"); if (optimstatus == GRB_OPTIMAL) { error = GRBgetdblattr(model, GRB_DBL_ATTR_OBJVAL, &objval); if (error) goto QUIT; printf("Optimal objective: %.4e\n\n", objval); } else if (optimstatus == GRB_INF_OR_UNBD) { printf("Model is infeasible or unbounded\n\n"); goto QUIT; } else if (optimstatus == GRB_INFEASIBLE) { printf("Model is infeasible\n\n"); goto QUIT; } else if (optimstatus == GRB_UNBOUNDED) { printf("Model is unbounded\n\n"); goto QUIT; } else { printf("Optimization was stopped with status = %d\n\n", optimstatus); goto QUIT; } /* Iterate over the solutions and compute the objectives */ error = GRBsetintparam(menv, "OutputFlag", 0); if (error) goto QUIT; error = GRBgetintattr(model, "SolCount", &solcount); if (error) goto QUIT; printf("\n"); for ( k = 0; k < solcount; ++k ) { error = GRBsetintparam(menv, "SolutionNumber", k); if (error) goto QUIT; error = GRBgetdblattr(model, GRB_DBL_ATTR_POOLOBJVAL, &objn); if (error) goto QUIT; printf("Solution %i has objective: %f\n", k, objn); } printf("\n"); error = GRBsetintparam(menv, "OutputFlag", 1); if (error) goto QUIT; /* Create a fixed model, turn off presolve and solve */ error = GRBfixmodel(model, &fixed); if (error || !fixed) { fprintf(stderr, "Error: could not create fixed model\n"); goto QUIT; } fenv = GRBgetenv(fixed); if (!fenv) { fprintf(stderr, "Error: could not get fixed model environment\n"); goto QUIT; } error = GRBsetintparam(fenv, "PRESOLVE", 0); if (error) goto QUIT; error = GRBoptimize(fixed); if (error) goto QUIT; error = GRBgetintattr(fixed, GRB_INT_ATTR_STATUS, &foptimstatus); if (error) goto QUIT; if (foptimstatus != GRB_OPTIMAL) { fprintf(stderr, "Error: fixed model isn't optimal\n"); goto QUIT; } error = GRBgetdblattr(fixed, GRB_DBL_ATTR_OBJVAL, &fobjval); if (error) goto QUIT; if (fabs(fobjval - objval) > 1.0e-6 * (1.0 + fabs(objval))) { fprintf(stderr, "Error: objective values are different\n"); } error = GRBgetintattr(model, "NumVars", &numvars); if (error) goto QUIT; /* Print values of nonzero variables */ for ( j = 0; j < numvars; ++j ) { error = GRBgetstrattrelement(fixed, "VarName", j, &varname); if (error) goto QUIT; error = GRBgetdblattrelement(fixed, "X", j, &x); if (error) goto QUIT; if (x != 0.0) { printf("%s %f\n", varname, x); } } QUIT: /* Error reporting */ if (error) { printf("ERROR: %s\n", GRBgeterrormsg(env)); exit(1); } /* Free models */ GRBfreemodel(model); GRBfreemodel(fixed); /* Free environment */ GRBfreeenv(env); return 0; }
