[Bug-glpk] glp_intopt recovery feature added

[Andrew Makhorin]

The internal routine ios_solve_node was changed to retry solving the
current subproblem with a new basis in case of simplex failure (mainly
due to singularity of the basis matrix which, in turn, may happen due to
inappropriate pivot choice). 
Thanks to Chris Matrakidis <address@hidden> for patch.

To fix the code please replace file glpk-4.58/src/glpios01.c with a new
one (see attachment).

Also attached is a model in free mps format that illustrates the effect.
(This model looks "innocent", but it has some pathological properties
that makes it very hard to solve with glpk.)


Andrew Makhorin

glpios01.c.gz
Description: GNU Zip compressed data

water.mps.gz
Description: GNU Zip compressed data