On Tue, Dec 29, 2009 at 9:03 AM, Andrew Makhorin <m...@gnu.org> wrote:
> > I am trying to solve a simple integer linear program
> > with the following constraints
>
> > x1 + x2 +x3 +x4 = 1
> > 10.00x1 + (-1.00)x2 < 5.00
> > 1.00x2 and +(-2.00)x3 < 5.00
> > 2.00x3 + (-0.50)x4 < 5.00
> > I have no objective function to optimise.
>
> > I am expecting output as x1 = 0 x2 = 1 x3 = 0 and x4 = 0
>
> > But when i solved using glpk 4.23 , i always get the output x1 = 0 x2 = 0
> x3 = 0 and x4 = 0
>
> > My code is as follows. Can somebody pls help me pointing out the problem.
>
> > int main()
> > {
> > glp_prob *lp;
> > int ia[1+1000], ja[1+1000];
> > double ar[1+1000];
> > int x1, x2, x3,x4;
> > ;
> >
> > outfile = fopen("lpout.out","w");
> > float cur1, cur2, cur3, cur4;
> > float bound_p, bound_q, bound_r;
> >
> >
> > glp_iocp parm;
> > glp_smcp simplex_parm;
> > int ret;
> >
> >
> > /*10.00x1 + (-1.00)x2 < 5.00
> > 1.00x2 and +(-2.00)x3 < 5.00
> > 2.00x3 + (-0.50)x4 < 5.00
> > */
> > lp = glp_create_prob();
> > glp_set_prob_name(lp, "sample");
> > glp_set_obj_dir(lp, GLP_MAX);
> >
> >
> > glp_add_rows(lp, 4);
> >
> > bound_p = 5 ;
> > bound_q = 5;
> > bound_r = 5 ;
> >
> > fprintf(outfile, "bound_p = %.2f bound_q %.2f bound_r = %.2f \n ",
> bound_p, bound_q, bound_r);
> >
> > glp_set_row_name(lp, 1, "p");
> > glp_set_row_bnds(lp, 1, GLP_UP, -DBL_MAX, bound_p);
> > glp_set_row_name(lp, 2, "q");
> > glp_set_row_bnds(lp, 2, GLP_UP, -DBL_MAX, bound_q);
> > glp_set_row_name(lp, 3, "r");
> > glp_set_row_bnds(lp, 3, GLP_UP, -DBL_MAX, bound_r);
> >
> > glp_set_row_name(lp, 4, "o");
> > glp_set_row_bnds(lp, 4, GLP_FX, 1, 1);
> >
> > glp_add_cols(lp, 4);
> > glp_set_col_name(lp, 1, "x1");
> > glp_set_col_bnds(lp, 1, GLP_DB, 0, 1);
> > glp_set_col_kind(lp, 1, GLP_IV);
> >
> > glp_set_col_name(lp, 2, "x2");
> > glp_set_col_bnds(lp, 2, GLP_DB, 0, 1);
> > glp_set_col_kind(lp, 2, GLP_IV);
> >
> > glp_set_col_name(lp, 3, "x3");
> > glp_set_col_bnds(lp, 3, GLP_DB, 0, 1);
> > glp_set_col_kind(lp, 3, GLP_IV);
> >
> > glp_set_col_name(lp, 4, "x4");
> > glp_set_col_bnds(lp, 4, GLP_DB, 0, 1);
> > glp_set_col_kind(lp, 4, GLP_IV);
> >
> >
> >
> > ia[1] = 2, ja[1] = 1, ar[1] = 10.0;
> > ia[2] = 2, ja[2] = 2, ar[2] = -1.0;
> > ia[3] = 2, ja[3] = 3, ar[3] = 0.0;
> > ia[4] = 2, ja[4] = 4, ar[4] = 0.0;
> >
> >
> >
> >
> > ia[5] = 3, ja[5] = 1, ar[5] = 0.0;
> > ia[6] = 3, ja[6] = 2, ar[6] = 1.0;
> > ia[7] = 3, ja[7] = 3, ar[7] = -2.0;
> > ia[8] = 3, ja[8] = 4, ar[8] = 0.0;
> >
> >
> > ia[9] = 4, ja[9] = 1, ar[9] = 0.0;
> > ia[10] = 4, ja[10] = 2, ar[10] = 0.0;
> > ia[11] = 4, ja[11] = 3, ar[11] = 2.0;
> > ia[12] = 4, ja[12] = 4, ar[12] = -0.5;
> >
> > fprintf(outfile, "x1 + x2 +x3 +x4 = 1 \n");
> > /*x1 + x2+ x3 + x4 = o */
> > ia[13] = 1, ja[13] = 1, ar[13] = 1;
> > ia[14] = 1, ja[14] = 2, ar[14] = 1;
> > ia[15] = 1, ja[15] = 3, ar[15] = 1;
> > ia[16] = 1, ja[16] = 4, ar[16] = 1;
> >
> > glp_load_matrix(lp, 16, ia, ja, ar);
> >
> > glp_init_smcp( simplex_parm);
> > simplex_parm.presolve = GLP_OFF;
> >
> > if(glp_simplex(lp, simplex_parm) != 0)
> > {
> > printf("failure of simplex\n");
> > exit(-1);
> > }
>
>
> >
> > x1 = glp_get_col_prim(lp, 1);
> > x2 = glp_get_col_prim(lp, 2);
> > x3 = glp_get_col_prim(lp, 3);
> > x4 = glp_get_col_prim(lp, 4);
> >
> > fprintf(outfile,"\n x1 = %d; x2 = %d; x3 = %d x4 = %d \n", x1, x2,
> x3, x4);
> >
> > glp_delete_prob(lp);
>
> > return 0;
> > }
> > The terminal output is
> > " 0: objval = 0.000000000e+00 infeas = 1.000000000e+00 (0)
> > 1: objval = 0.000000000e+00 infeas = 0.000000000e+00 (0)
> > OPTIMAL SOLUTION FOUND"
>
> > Thanks,
> > satish
>
> Looks like you missed the very first constraint.
>
(So did I in my earlier comment, oops)
>
> Once you have built your instance, you can write it to a text file
> in cplex lp format for visual inspection:
>
> glp_write_lp(lp, NULL, "foobar.lp");
>
> This also allows running your instance with the glpsol stand-alone
> solver:
>
> $ glpsol --cpxlp foobar.lp
>
> FYI: the most recent version of glpk is 4.41.
>
>
>
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> Help-glpk mailing list
> Help-glpk@gnu.org
> http://lists.gnu.org/mailman/listinfo/help-glpk
>
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