-------- Forwarded Message -------- From: Horst Schirmeier <[email protected]> To: Andrew Makhorin <[email protected]> Cc: [email protected] Subject: Re: Simplex termination 32 vs. 64 bit Date: Mon, 9 Apr 2012 23:36:46 +0200
On Tue, 10 Apr 2012, Andrew Makhorin wrote: > > [...] > > The input data is attached to this email. Is it somewhat malformed, or > > did I indeed step on a GLPK bug? > > No, this is not a bug. > > The point is that glpk uses floating-point calculations that are > sensitive to many platform-dependent factors (compiler options, etc.). > That means that you may expect to obtain identical results only on > identical platforms. In particular, you may note that 32-bit version > performed 851 simplex iterations to solve the lp relaxation while 64-bit > one performed 844 iterations. > > Your mip instance is generally hard for the branch-and-bound solver > (used by default), and it was solved quickly with the 64-bit version for > a happy chance. However, I think that the branch-and-cut solver with the > mir cuts enabled (--mir) is able to solve your mip for a short time > independently on the platform used: > [...] > > The Gomory cuts (--gomory) also seem to be efficient: > [...] Thanks for clearing this up. Now I need to read up on MIR / Gomory cuts to decide whether I can expect these to be the right choice for my whole problem class; these ILPs are part of an automated process. Thanks! Kind regards, Horst Schirmeier _______________________________________________ Bug-glpk mailing list [email protected] https://lists.gnu.org/mailman/listinfo/bug-glpk
