> I am using the glpk C API to solve real linear programming > problems with > the simplex algorithm and I am encountering a problem potentially > originating from the glpk library. The program crashes telling: > Assertion failed: ap[q] != 0.0; file glpspx1.c; line 1525 > Writing the problem in .mps file (attached to the email) and > using > glpsol reproduces the error ( glpsol prob.mps --max ) . > I haven't investigated that much the linear problem, it may be > infeasible, but previous infeasible problems had been correctly > detected > by glpk.
I run your instance with glpsol 4.8 using various options, however, could not catch the error. The most stable results were obtained using options --max --nopresol --noscale: lpx_read_mps: reading problem data from `prob.mps'... lpx_read_mps: problem name not specified lpx_read_mps: 1162 rows, 713 columns, 4538 non-zeros lpx_read_mps: 3637 cards were read lpx_adv_basis: size of triangular part = 1124 0: objval = 0.000000000e+00 infeas = 1.000000000e+00 (31) 200: objval = 0.000000000e+00 infeas = 4.201680672e-03 (20) 237: objval = 0.000000000e+00 infeas = 1.387626018e-13 (15) * 237: objval = 0.000000000e+00 infeas = 3.302549922e-11 (15) * 250: objval = 1.519754903e+04 infeas = 1.196406822e-09 (15) PROBLEM HAS UNBOUNDED SOLUTION Time used: 1.0 secs Memory used: 1.0M (1056492 bytes) I think the error appears due to the same reason as explained in two messages you found on the list, i.e. because glpk simplex solver is not robust and sometimes numerical difficulties cause its crashing. Try to change some options (e.g. --noscale, --nopresol, --std, etc.). Andrew Makhorin _______________________________________________ Help-glpk mailing list Help-glpk@gnu.org http://lists.gnu.org/mailman/listinfo/help-glpk