[Help-glpk] Re: How to solve a simple MIP problem ?

[Andrew Makhorin]

>I want to solve a simple problem MIP (I guess) using GLPK API, but
> I couldn't find some samples to help me.
>My problem is:
>
>    Minimize: x0
>
>Where:
>    x0 -p + b >= 0
>    x0 -p -f >= -1
>    b = 1
>    f = 1
>
>x0, b, f and p are all binary variables.
>
>I've tried to change te code that cames with manual but didn't work...
>More I change, more problems show up.
>Someone could send me a simple C code that solve it?

Here is an example below.

#include "glpk.h"

#define row_1     1
#define row_2     2

#define col_x0    1
#define col_p     2
#define col_b     3
#define col_f     4

int main(void)
{     LPX *prob;
      int ndx[1000];
      double val[1000];
      prob = lpx_create_prob();
      lpx_set_class(prob, LPX_MIP);
      lpx_add_rows(prob, 3);
      lpx_add_cols(prob, 4);
      /* x0 - p + b >= 0 */
      ndx[1] = col_x0, val[1] = 1;
      ndx[2] = col_p, val[2] = -1;
      ndx[3] = col_b, val[3] = 1;
      lpx_set_mat_row(prob, row_1, 3, ndx, val);
      lpx_set_row_bnds(prob, row_1, LPX_LO, 0, 0);
      /* x0 - p - f >= -1 */
      ndx[1] = col_x0, val[1] = 1;
      ndx[2] = col_p, val[2] = -1;
      ndx[3] = col_f, val[3] = -1;
      lpx_set_mat_row(prob, row_2, 3, ndx, val);
      lpx_set_row_bnds(prob, row_2, LPX_LO, -1, 0);
      /* all variables are binary */
      lpx_set_col_bnds(prob, col_x0, LPX_DB, 0, 1);
      lpx_set_col_kind(prob, col_x0, LPX_IV);
      lpx_set_col_bnds(prob, col_p, LPX_DB, 0, 1);
      lpx_set_col_kind(prob, col_p, LPX_IV);
      lpx_set_col_bnds(prob, col_b, LPX_DB, 0, 1);
      lpx_set_col_kind(prob, col_b, LPX_IV);
      lpx_set_col_bnds(prob, col_f, LPX_DB, 0, 1);
      lpx_set_col_kind(prob, col_f, LPX_IV);
      /* minimize x0 */
      lpx_set_obj_dir(prob, LPX_MIN);
      lpx_set_col_coef(prob, col_x0, 1);
      /* solve lp relaxation */
      lpx_simplex(prob);
      /* solve mip */
      lpx_integer(prob);
      /* print mip solution */
      lpx_print_mip(prob, "sol.txt");
      lpx_delete_prob(prob);
      return 0;
}