[Help-glpk] Incorrect solution via library interface

[Uday Reddy]

I have glpk-4.52.1-2.fc20.x86_64. For the attached ILP, when using
glpk as a library with a simple interfacing code (also attached), I
get an incorrect all zero solution (2nd and 4th constraints from the
bottom are violated).

----------------------------------------------------------------------------------------------------
$ gcc unit_test_glpk.c -lglpk -lm
$ ./a.out
Reading problem data from 'test.cplex'...
32 rows, 11 columns, 62 non-zeros
11 integer variables, 2 of which are binary
62 lines were read
Scaling...
 A: min|aij| =  1.000e+00  max|aij| =  1.002e+06  ratio =  1.002e+06
GM: min|aij| =  1.778e-01  max|aij| =  5.625e+00  ratio =  3.164e+01
EQ: min|aij| =  3.161e-02  max|aij| =  1.000e+00  ratio =  3.164e+01
Constructing initial basis...
Size of triangular part is 32
GLPK Simplex Optimizer, v4.52
32 rows, 11 columns, 62 non-zeros
Preprocessing...
14 rows, 8 columns, 44 non-zeros
Scaling...
 A: min|aij| =  1.000e+00  max|aij| =  1.002e+06  ratio =  1.002e+06
GM: min|aij| =  1.778e-01  max|aij| =  5.625e+00  ratio =  3.164e+01
EQ: min|aij| =  3.161e-02  max|aij| =  1.000e+00  ratio =  3.164e+01
Constructing initial basis...
Size of triangular part is 14
      0: obj =  -3.000000000e+03  infeas =  5.602e+03 (0)
*     6: obj =   1.502550000e+04  infeas =  0.000e+00 (0)
*    11: obj =  -1.110482799e-32  infeas =  5.136e-34 (0)
OPTIMAL LP SOLUTION FOUND
GLPK Integer Optimizer, v4.52
32 rows, 11 columns, 62 non-zeros
11 integer variables, 2 of which are binary
Integer optimization begins...
+    11: mip =     not found yet >=              -inf        (1; 0)
+    11: >>>>>   0.000000000e+00 >=   0.000000000e+00   0.0% (1; 0)
+    11: mip =   0.000000000e+00 >=     tree is empty   0.0% (0; 1)
INTEGER OPTIMAL SOLUTION FOUND
z = 0.000000
c0 = 0, c1 = 0, c2 = 0, c3 = 0, c4 = 0, c5 = 0, c6 = 0, c7 = 0, c8 =
0, c9 = 0, c10 = 0,
--------------------------------------------------------------------------------------------------

However, with the standalone tool, I get the right one.

glpsol --lp test.cplex -o sol

cat sol
[...]
   No. Column name       Activity     Lower bound   Upper bound
------ ------------    ------------- ------------- -------------
     1 c_0          *              1             0
     2 c_1          *              0             0
     3 c_2          *              0             0
     4 c_3          *              1             0             3
     5 c_4          *             -1         -1000          1000
     6 c_5          *              0         -1000          1000
     7 c_6          *              0             0          1000
     8 c_7          *              0             0          1000
     9 c_8          *              0             0
    10 c_9          *              0             0             1
    11 c_10         *              0             0             1

Anything wrong with this simple library interface?

Thanks.


    glp_prob *lp = glp_create_prob();

    glp_read_lp(lp, NULL, "test.cplex");

    glp_smcp parm;
    glp_init_smcp(&parm);
    parm.presolve = GLP_ON;

    glp_scale_prob(lp, GLP_SF_AUTO);
    glp_adv_basis(lp, 0);
    glp_simplex(lp, &parm);

    int lp_status = glp_get_status(lp);

    if (lp_status == GLP_NOFEAS) {
        glp_delete_prob(lp);
        return 1;
    }

    glp_intopt(lp, NULL);

    int ilp_status = glp_mip_status(lp);

    if (ilp_status == GLP_NOFEAS) {
        glp_delete_prob(lp);
        return 1;
    }

    double z = glp_mip_obj_val(lp);
    printf("z = %lf\n", z);

    for (j=0; j<glp_get_num_cols(lp); j++) {
        double x = glp_mip_col_val(lp, j+1);
        printf("c%d = %lld, ", j, (int64) round(x));
    }
    printf("\n");;
    glp_delete_prob(lp);

unit_test_glpk.c
Description: Text Data

test.cplex
Description: Binary data