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


From: Andrew Makhorin
Subject: [Bug-glpk] [Fwd: Bug report GLPK Version 4.43]
Date: Wed, 17 Aug 2011 00:39:16 +0400

-------- Forwarded Message --------
From: Robert Peharz <address@hidden>
To: address@hidden
Subject: Bug report GLPK Version 4.43
Date: Tue, 16 Aug 2011 19:15:24 +0200

Hi,

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.

Best regards, Robert Peharz





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