Re: [Bug-glpk] [Fwd: Bug report GLPK Version 4.43]

[Andrew Makhorin]

> I think there is a bug concerning the MILP solver in GLPK version 4.43.
> I deactivated the MILP presolver, and explicitly provided a valid basis
> by running the simplex method first, followed by glp_intopt:
> 
> retSIMP = glp_simplex(lp, &simplexParams);
> retMILP = glp_intopt(lp, &milpParams);
> 
> Occasionally it happens that the MILP solver does not need to branch
> (i.e. the MILP callback function is never called with
> glp_ios_reason(tree) == GLP_IBRANCH), but an integer solution is found
> merely using (Gomory) cutting planes. In these cases, glp_intopt does
> not return the integer solution, but the initial, relaxed solution as
> found by the simplex method.
> I am not sure, if this also happens when the MILP presolver is activated.

Please check that you retrieve mip solution components with
glp_mip_row/col_val, not with glp_get_row/col_prim (the latter is used
to retrieve components of basic solution). I don't think that this is 
a bug, because glp_intopt stores to the problem object only integer
feasible solutions. Thanks.

Andrew Makhorin