-------- Forwarded Message -------- From: Rafael Korbaš <[email protected]> To: [email protected] Subject: glpk_intopt loops forever on a specific input when MIP presolver enabled Date: Tue, 7 Nov 2017 18:18:09 +0300
Hello, I'm using the latest version of your library (4.63) and I came across a specific LP problem instance, that causes looping forever when the MIP presolver is enabled. I'm sending you the problem definition in the attachment (problem.lp file). You should be able to replicate the behavior by executing the CLI of your library. I include the commands I tried: My first approach: "glpsol --lp problem.lp" -> loops forever with the warning "Warning: numerical instability (primal simplex, phase II)" So I assumed that maybe it is due to poor scaling, so I tried: "glpsol --lp --scale problem.lp" -> loops forever the same way So I tried disabling the presolver, but still no luck: "glpsol --lp --scale --nopresol problem.lp" -> loops forever the same way So I tried disabling the MIP presolver and finally, I got the result: "glpsol --lp --scale --nopresol --nointopt problem.lp" -> finally gave a result Also "glpsol --lp --nointopt problem.lp" works which points to the MIP presolver as the "faulty" part. Could you explain me why the involvement of the MIP presolver causes such behavior? Is it a bug or is my LP problem instance just poorly defined? If it is poorly defined, how to correct the problem definition by the operations available in your library (like scaling, presolving, ...) without losing precision? Best regards, Rafael
problem.lp
Description: Binary data
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