[Bug-glpk] assertion b>0 in glplpx12.c::796 fail

[Stefan Vigerske]

Hi,

in some seldom situations GLPK fails with an "internal error" when it
tries to generate a mixed cover cut.
Unfortunately, I did not manage to generate a mps file for reproduction
(the problem appears inside a B&B, and with a generated mps file, it is
working fine), so I send you only the output.
Maybe you have some idea under which circumstances b could be smaller or
equal 0 and let the GLPK solve return with some error code. :-)

ipp_basic_tech:  0 row(s) and 0 column(s) removed
ipp_reduce_bnds: 2 pass(es) made, 14 bound(s) reduced
ipp_basic_tech:  0 row(s) and 0 column(s) removed
ipp_reduce_coef: 1 pass(es) made, 0 coefficient(s) reduced
lpx_intopt: presolved MIP has 68 rows, 72 columns, 226 non-zeros
lpx_intopt: 16 integer columns, 10 of which are binary
lpx_adv_basis: size of triangular part = 68
Solving LP relaxation...
      0:   objval =   2.425852301e+08   infeas =   1.000000000e+00 (0)
     25:   objval =   3.735170535e+08   infeas =   0.000000000e+00 (0)
*    25:   objval =   3.735170535e+08   infeas =   0.000000000e+00 (0)
*    48:   objval =   6.588564313e+04   infeas =   0.000000000e+00 (0)
OPTIMAL SOLUTION FOUND
Creating the conflict graph...
The conflict graph is either empty or too big
Generating cutting planes...
&    48: obj =   6.588564313e+04   frac =    12   cuts =     0 (0)
GLPK internal error: b > 0.0; file
../../../GAMSlinks-trunk/ThirdParty/Glpk/glpk/src/glplpx12.c, line 796

Best,
Stefan