Re: [Help-glpk] glp_find_col

[Andrew Makhorin]

On Fri, 2015-09-04 at 11:06 +0200, Yaser Tohidi wrote:
> No, I have assigned a name to jth column. When I print "name" the name
> of jth column is shown.
> The problem is that I want to use glp_find _col. I use the same "name"
> coming from glp_get_col_name but glp_find_col returns zero.
> I hope it's clear now.
> 
> On Thu, Sep 3, 2015 at 8:53 PM, Andrew Makhorin <address@hidden> wrote:
>         On Thu, 2015-09-03 at 16:36 +0200, Yaser Tohidi wrote:
>         > I cannot use "glp_find_col". It retrieves zero always even I
>         use the
>         > following code. I also create index at the beginning by
>         > glp_create-index.
>         >
>         >
>         > const char *name;
>         > name= glp_get_col_name(lp1,j);
>         > i=glp_find_col(lp1,name);
>         >
>         >
>         >
>         > Please let me know what I'm missing.
>         >
>         
>         
>         Looks like you didn't assign a name to j-th column, so
>         glp_get_col_name
>         returns NULL.
>         
>         
>         
> 
> 

Please check you code. The following example works fine for me:

/* sample.c */

#include <stdio.h>
#include <stdlib.h>
#include <glpk.h>

int main(void)
{     glp_prob *lp;
      int ia[1+1000], ja[1+1000];
      double ar[1+1000], z, x1, x2, x3;
s1:   lp = glp_create_prob();
s2:   glp_set_prob_name(lp, "sample");
s3:   glp_set_obj_dir(lp, GLP_MAX);
s4:   glp_add_rows(lp, 3);
s5:   glp_set_row_name(lp, 1, "p");
s6:   glp_set_row_bnds(lp, 1, GLP_UP, 0.0, 100.0);
s7:   glp_set_row_name(lp, 2, "q");
s8:   glp_set_row_bnds(lp, 2, GLP_UP, 0.0, 600.0);
s9:   glp_set_row_name(lp, 3, "r");
s10:  glp_set_row_bnds(lp, 3, GLP_UP, 0.0, 300.0);
s11:  glp_add_cols(lp, 3);
s12:  glp_set_col_name(lp, 1, "x1");
s13:  glp_set_col_bnds(lp, 1, GLP_LO, 0.0, 0.0);
s14:  glp_set_obj_coef(lp, 1, 10.0);
s15:  glp_set_col_name(lp, 2, "x2");
s16:  glp_set_col_bnds(lp, 2, GLP_LO, 0.0, 0.0);
s17:  glp_set_obj_coef(lp, 2, 6.0);
s18:  glp_set_col_name(lp, 3, "x3");
s19:  glp_set_col_bnds(lp, 3, GLP_LO, 0.0, 0.0);
s20:  glp_set_obj_coef(lp, 3, 4.0);
s21:  ia[1] = 1, ja[1] = 1, ar[1] =  1.0; /* a[1,1] =  1 */
s22:  ia[2] = 1, ja[2] = 2, ar[2] =  1.0; /* a[1,2] =  1 */
s23:  ia[3] = 1, ja[3] = 3, ar[3] =  1.0; /* a[1,3] =  1 */
s24:  ia[4] = 2, ja[4] = 1, ar[4] = 10.0; /* a[2,1] = 10 */
s25:  ia[5] = 3, ja[5] = 1, ar[5] =  2.0; /* a[3,1] =  2 */
s26:  ia[6] = 2, ja[6] = 2, ar[6] =  4.0; /* a[2,2] =  4 */
s27:  ia[7] = 3, ja[7] = 2, ar[7] =  2.0; /* a[3,2] =  2 */
s28:  ia[8] = 2, ja[8] = 3, ar[8] =  5.0; /* a[2,3] =  5 */
s29:  ia[9] = 3, ja[9] = 3, ar[9] =  6.0; /* a[3,3] =  6 */
s30:  glp_load_matrix(lp, 9, ia, ja, ar);
s31:  glp_simplex(lp, NULL);
s32:  z = glp_get_obj_val(lp);
s33:  x1 = glp_get_col_prim(lp, 1);
s34:  x2 = glp_get_col_prim(lp, 2);
s35:  x3 = glp_get_col_prim(lp, 3);
s36:  printf("\nz = %g; x1 = %g; x2 = %g; x3 = %g\n",
         z, x1, x2, x3);
#if 1
      {   int j;
          const char *name;
          glp_create_index(lp);
          for (j = 1; j <= 3; j++)
          {  name = glp_get_col_name(lp, j);
             printf("name = |%s| find_col = %d\n",
                name, glp_find_col(lp, name));
          }
      }
#endif
s37:  glp_delete_prob(lp);
      return 0;
}

/* eof */

address@hidden:~/Desktop$ gcc sample.c -lglpk
address@hidden:~/Desktop$ ./a.out
GLPK Simplex Optimizer, v4.45
3 rows, 3 columns, 9 non-zeros
*     0: obj =   0.000000000e+00  infeas =  0.000e+00 (0)
*     2: obj =   7.333333333e+02  infeas =  0.000e+00 (0)
OPTIMAL SOLUTION FOUND

z = 733.333; x1 = 33.3333; x2 = 66.6667; x3 = 0
name = |x1| find_col = 1
name = |x2| find_col = 2
name = |x3| find_col = 3
address@hidden:~/Desktop$