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RE: [Help-glpk] Understanding the LPX_K_TOLOBJ parameter

From: Joey Rios
Subject: RE: [Help-glpk] Understanding the LPX_K_TOLOBJ parameter
Date: Sat, 23 Feb 2008 09:34:58 -0800

> > In CPLEX, I'd set the
> > mipgap value appropriately.  After reading through the GLPK manual,

> Do not change tol_obj. Set the relative mip gap, say, to 0.01 (that
> means 1%) to prematurely stop the search. In this case you obtain
> a suboptimal solution. Besides, you can try enabling cutting planes;
> sometimes this helps to reduce the solution time.

I am using GLPK 4.26, but the manual I printed as reference some time ago was from GLPK 4.21.  Looks like in between that time you implemented the LPX_K_MIPGAP parameter (in release 4.23).  That's why I didn't try using it, I didn't know it was there!  Thanks for the quick response.  I'll try both the correct parameter and the cutting planes when I get to work on Monday.

As an aside on this topic, I've seen where CPLEX (or AMPL?) publishes a short (but growing) list of changes with each release.  Something like:

Keywords added for CPLEX 6.5


Keywords no longer available


Keywords added for CPLEX 7.0


An example of what I mean is seen toward the bottom of this page:

Maybe we could get something like this for GLPK.  So in addition to your full descriptions of changes with each release, the release itself would have this updated list?  Then when there is a new version, I could just print out that page and attach to my manual, instead of printing the whole manual again.  If a new keyword/parameter/function looks appropriate/interesting, I could then follow-up on my own and find out more about it.  This type of list might have saved me with this particular problem and I am sure could be helpful to others.

I know you already do a lot of work with this package, Andrew, and it is appreciated.  This is just a little suggestion to take or leave.

Thanks again,

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