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Re: [Bug-glpk] Infinite loop

From: Andrew Makhorin
Subject: Re: [Bug-glpk] Infinite loop
Date: Thu, 13 Jul 2006 17:25:17 +0400

> I encountered a situation where I got into an infinite loop in the
> routine spx_simplex in the module glpspx2.c. The call to the
> function spx_prim_feas located shortly after the feas: label
> returned LPX_E_OK and control passed to the label opt:. The call to
> the routine spx_prim_opt returned LPX_E_INSTAB which transferred
> control back to label feas:. This sequence then repeated without
> end.

> I changed the case statement after the spx_prim_opt call such that
> the LPX_E_INSTAB return goes to label done: instead of feas:.

glp_simplex switches to the phase I if the current basic solution
becomes primal infeasible within a tolerance, that sometimes may
lead to an infinite loop. This is a lack of implementation.

I hope to finish soon a new, more robust and faster simplex code,
which will be included in glpk as a basic lp solver.

Andrew Makhorin

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