Re: [Help-glpk] Easiest interface

[Andrew Makhorin]

> Hi all, not sure if this is the right forum to ask that question, but
> will try anyway.

> I am planning on doing a short workshop on approximation algorithms,
> including LP based methods for talented high school students and I
> would like to give them some simple programming tasks to get the
> flavour of how LP based methods work. The problem is I will not have
> much time and I am wondering if there exists some sort of easy to
> grasp interface to glpk, so that you can easily get going in, say,
> 10-20 minutes, assuming you have a decent grasp of C/C++. I myself use
> glpk directly, but I remember that it was a bit hard at the beginning.
> Also, maybe a different tool would be a better choice? However we will
> postprocess the results of the LP solver, so it is important that the
> tool works non-interactively.

Below here is an easy example of application program using glpk api.
It reads lp instance from a text file in cplex lp format, solves it
with the primal simplex, and writes optimal solution to a text file in
printable format. Probably it might be a starting point for beginners.

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

int main(int argc, char *argv[])
{     glp_prob *P;
      int ret;
      if (argc != 2)
      {  printf("Usage: %s lp-file\n", argv[0]);
         return 0;
      }
      P = glp_create_prob();
      ret = glp_read_lp(P, NULL, argv[1]);
      if (ret != 0) return 1;
      glp_simplex(P, NULL);
      glp_print_sol(P, "sol");
      glp_delete_prob(P);
      return 0;
}

Reading problem data from `plan.lp'...
8 rows, 7 columns, 48 non-zeros
39 lines were read
GLPK Simplex Optimizer, v4.43
8 rows, 7 columns, 48 non-zeros
      0: obj =   8.000000000e+01  infeas =  2.811e+03 (1)
*     4: obj =   4.376770833e+02  infeas =  0.000e+00 (0)
*    10: obj =   2.962166065e+02  infeas =  0.000e+00 (0)
OPTIMAL SOLUTION FOUND
Writing basic solution to `sol'...

(Example lp data file 'plan.lp' is included in the distribution and
can be found in subdirectory glpk/examples.)