gurobi example in c

/* 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"

#define GUR_INITIAL 0
#define GUR_DONE_ENV 1
#define GUR_DONE_MODEL 2

#define GRP_EXIT_NORMAL 0
#define GRP_EXIT_LIBRARY_ERROR 1
#define GRP_EXIT_SOLVE_UNFEASABLE 2
#define GRP_EXIT_ABORT 3

#define GRB_EXCEPTION_EXIT(env,model,state)                                               \
do {                                                                                      \
    printf("ERROR: %s\n", GRBgeterrormsg(env));                                           \
    if (state == GUR_DONE_MODEL)  GRBfreemodel(model);   /* Free model */                 \
    if (state == GUR_DONE_ENV)  GRBfreeenv(env);        /* Free environment */            \
    exit(GRP_EXIT_LIBRARY_ERROR);                                                         \
} while(0);

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;
  int state = GUR_INITIAL;
  int ret = GRP_EXIT_NORMAL;

  /* Create environment */

  error = GRBloadenv(&env, "sos.log");
  if (error) GRB_EXCEPTION_EXIT(env,model,state)
  state = GUR_DONE_ENV;

  /* Create an empty model */

  error = GRBnewmodel(env, &model, "sos", 0, NULL, NULL, NULL, NULL, NULL);
  if (error) EXCEPTION_EXIT(env,model,state);
  state = GUR_DONE_MODEL;

  /* 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) EXCEPTION_EXIT(env,model,state);

  /* 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) EXCEPTION_EXIT(env,model,state);

  /* Optimize model */

  error = GRBoptimize(model);
  if (error) EXCEPTION_EXIT(env,model,state);

  /* Write model to 'sos.lp' */

  error = GRBwrite(model, "sos.lp");
  if (error) EXCEPTION_EXIT(env,model,state);

  /* Capture solution information */

  error = GRBgetintattr(model, GRB_INT_ATTR_STATUS, &optimstatus);
  if (error) EXCEPTION_EXIT(env,model,state);

  error = GRBgetdblattr(model, GRB_DBL_ATTR_OBJVAL, &objval);
  if (error) EXCEPTION_EXIT(env,model,state);

  error = GRBgetdblattrarray(model, GRB_DBL_ATTR_X, 0, 3, x);
  if (error) EXCEPTION_EXIT(env,model,state);

  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");
    ret = GRP_EXIT_SOLVE_UNFEASABLE;
  } else {
    printf("Optimization was stopped early\n");
    ret = GRP_EXIT_ABORT;
  }

  GRBfreemodel(model);   /* Free model */
  GRBfreeenv(env);       /* Free environment */

  return ret;
}