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Re: [Help-glpk] glpk 4.9 release information

From: Andrew Makhorin
Subject: Re: [Help-glpk] glpk 4.9 release information
Date: Thu, 26 Jan 2006 13:49:04 +0300

>> The lower bound obtained from a relaxation is only a bound. Its value
>> may depend, for example, on transformations performed by presolver or
>> on cutting planes added to the relaxation. So it does not express any
>> essential information.
> I agree with you, but when using cplex I use it as an indication of the 
> progress of the solver. If the lower bound only changes in, say, the 12th 
> digit it is quite likely that the solver will run out of memory before the 
> optimal solution is found. So if it would be possible to optionally print 
> it I would most likely use it for this kind of thing.

In most cases the lower bound does not increases smoothly; it keeps
its value until corresponding node has been pruned, so it is not a good
indicator of the progress. In glpk a better indication is the number of
active and fathomed nodes displayed in parentheses. If the number of
active nodes increases much faster than the number of fathomed nodes for
a long time (say, one hour), the problem is hard for glpk solver.

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