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sos_c.c
/* Copyright 2020, Gurobi Optimization, LLC */
/* This example creates a very simple Special Ordered Set (SOS) model.
The model consists of 3 continuous variables, no linear constraints,
and a pair of SOS constraints of type 1. */
#include <stdlib.h>
#include <stdio.h>
#include "gurobi_c.h"
int
main(int argc,
char *argv[])
{
GRBenv *env = NULL;
GRBmodel *model = NULL;
int error = 0;
double x[3];
double obj[3];
double ub[3];
int sostype[2];
int sosbeg[2];
int sosind[4];
double soswt[4];
int optimstatus;
double objval;
/* Create environment */
error = GRBloadenv(&env, "sos.log");
if (error) goto QUIT;
/* Create an empty model */
error = GRBnewmodel(env, &model, "sos", 0, NULL, NULL, NULL, NULL, NULL);
if (error) goto QUIT;
/* Add variables */
obj[0] = -2; obj[1] = -1; obj[2] = -1;
ub[0] = 1.0; ub[1] = 1.0; ub[2] = 2.0;
error = GRBaddvars(model, 3, 0, NULL, NULL, NULL, obj, NULL, ub, NULL,
NULL);
if (error) goto QUIT;
/* Build first SOS1: x0=0 or x1=0 */
sosind[0] = 0; sosind[1] = 1;
soswt[0] = 1.0; soswt[1] = 2.0;
sosbeg[0] = 0; sostype[0] = GRB_SOS_TYPE1;
/* Build second SOS1: x0=0 or x2=0 */
sosind[2] = 0; sosind[3] = 2;
soswt[2] = 1.0; soswt[3] = 2.0;
sosbeg[1] = 2; sostype[1] = GRB_SOS_TYPE1;
/* Add SOSs to model */
error = GRBaddsos(model, 2, 4, sostype, sosbeg, sosind, soswt);
if (error) goto QUIT;
/* Optimize model */
error = GRBoptimize(model);
if (error) goto QUIT;
/* Write model to 'sos.lp' */
error = GRBwrite(model, "sos.lp");
if (error) goto QUIT;
/* Capture solution information */
error = GRBgetintattr(model, GRB_INT_ATTR_STATUS, &optimstatus);
if (error) goto QUIT;
error = GRBgetdblattr(model, GRB_DBL_ATTR_OBJVAL, &objval);
if (error) goto QUIT;
error = GRBgetdblattrarray(model, GRB_DBL_ATTR_X, 0, 3, x);
if (error) goto QUIT;
printf("\nOptimization complete\n");
if (optimstatus == GRB_OPTIMAL) {
printf("Optimal objective: %.4e\n", objval);
printf(" x=%.4f, y=%.4f, z=%.4f\n", x[0], x[1], x[2]);
} else if (optimstatus == GRB_INF_OR_UNBD) {
printf("Model is infeasible or unbounded\n");
} else {
printf("Optimization was stopped early\n");
}
QUIT:
/* Error reporting */
if (error) {
printf("ERROR: %s\n", GRBgeterrormsg(env));
exit(1);
}
/* Free model */
GRBfreemodel(model);
/* Free environment */
GRBfreeenv(env);
return 0;
}
