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### mip1_c.c

/* Copyright 2021, Gurobi Optimization, LLC */

/* This example formulates and solves the following simple MIP model:

maximize    x +   y + 2 z
subject to  x + 2 y + 3 z <= 4
x +   y       >= 1
x, y, z binary
*/

#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    sol[3];
int       ind[3];
double    val[3];
double    obj[3];
char      vtype[3];
int       optimstatus;
double    objval;

/* Create environment */
error = GRBemptyenv(&env);
if (error) goto QUIT;

error = GRBsetstrparam(env, "LogFile", "mip1.log");
if (error) goto QUIT;

error = GRBstartenv(env);
if (error) goto QUIT;

/* Create an empty model */
error = GRBnewmodel(env, &model, "mip1", 0, NULL, NULL, NULL, NULL, NULL);
if (error) goto QUIT;

/* Add variables */
obj[0] = 1; obj[1] = 1; obj[2] = 2;
vtype[0] = GRB_BINARY; vtype[1] = GRB_BINARY; vtype[2] = GRB_BINARY;
error = GRBaddvars(model, 3, 0, NULL, NULL, NULL, obj, NULL, NULL, vtype,
NULL);
if (error) goto QUIT;

/* Change objective sense to maximization */
error = GRBsetintattr(model, GRB_INT_ATTR_MODELSENSE, GRB_MAXIMIZE);
if (error) goto QUIT;

/* First constraint: x + 2 y + 3 z <= 4 */
ind[0] = 0; ind[1] = 1; ind[2] = 2;
val[0] = 1; val[1] = 2; val[2] = 3;

error = GRBaddconstr(model, 3, ind, val, GRB_LESS_EQUAL, 4.0, "c0");
if (error) goto QUIT;

/* Second constraint: x + y >= 1 */
ind[0] = 0; ind[1] = 1;
val[0] = 1; val[1] = 1;

error = GRBaddconstr(model, 2, ind, val, GRB_GREATER_EQUAL, 1.0, "c1");
if (error) goto QUIT;

/* Optimize model */
error = GRBoptimize(model);
if (error) goto QUIT;

/* Write model to 'mip1.lp' */
error = GRBwrite(model, "mip1.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, sol);
if (error) goto QUIT;

printf("\nOptimization complete\n");
if (optimstatus == GRB_OPTIMAL) {
printf("Optimal objective: %.4e\n", objval);

printf("  x=%.0f, y=%.0f, z=%.0f\n", sol[0], sol[1], sol[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;
}


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