[Bug-glpk] bug in spx_prim_chuzr and solution

[Kiriakos Vlahos]

I found a rather rare bug in spx_prim_chuzr.

If all elements of the q-th column of the simplex table are too small,
ret is set to 1 to tell the calling routine to reinvert the basis (which
is currently not implemented and causes an error).

But if (typx[k] == LPX_DB) this is OK and should not cause concern.

I suggest the following modification at line 740:

      if (typx[k] == LPX_DB)
      {  /* xN[q] has both lower and upper bounds */
         p = -1, p_tag = 0, teta = (ub[k] - lb[k]) + relax, big = 1.0;
         ret = 0; //<- added line
      }

This logic error may exist in similar routines used in the dual variant
of the simplex method but I have not checked.  I came across it while
solving a very simple problem with one constraint!

Many thanks

Kiriakos Vlahos