[Coin-osi-devel] More params, glpk 4.9, mip gap

Brady Hunsaker hunsaker at engr.pitt.edu
Mon Apr 10 11:01:54 EDT 2006


Thanks for your interest and contribution.  In the release notes in GLPK
4.9, the author stated that in some cases lpx_integer does better than
lpx_intopt, but my understanding is that lpx_intopt is expected to be
better more often--at least on hard instances.  So it probably makes
sense to switch to it in OsiGlpk.  I just haven't made the time to make
the change and test it yet.

Does this affect your AMPL interface at all?  It seems that if you are
using OSI routines, then it shouldn't matter what's happening behind the


Kendall Bailey wrote:
> I'm preparing to submit an AMPL driver program to the COIN project,
> based on OSI solvers.  I've added a boolean attribute to the OsiGlpk
> class to select the branch and bound routine to invoke.  My goal is to
> simply expose as much solver functionality to AMPL as I can.  I've
> made the AMPL driver (I'm calling it 'coinamp' similar to ILOGs
> 'cplexamp') makefile able to disable the use of the new boolean, so
> when I submit the code others can build it against a stock OsiGlpk. 
> Do you have plans to make the lpx_intopt() function callable from
> OsiGlpk's branchAndBound()?  Do you want a patch?  Is lpx_intopt()
> always better than lpx_integer() and OsiGlpk should just switch over?
> Thanks,
> Kendall Bailey
> On 3/16/06, Brady Hunsaker <hunsaker at engr.pitt.edu> wrote:
>> In the specific case of the two integer optimization routines, I haven't
>> yet looked at updating OsiGlpk for GLPK 4.9.  It may make sense to
>> change the branchAndBound call so that the new routine is the default.
>> I know this doesn't address the question of allowing users their choice
>> of routines, however.
>> Brady
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Brady Hunsaker
Assistant Professor
Industrial Engineering
University of Pittsburgh

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