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[Bug-glpk] [Fwd: Inconsistent run times]


From: Andrew Makhorin
Subject: [Bug-glpk] [Fwd: Inconsistent run times]
Date: Tue, 30 Oct 2012 23:20:29 +0400

-------- Forwarded Message --------
From: Marc Goetschalckx <address@hidden>
To: address@hidden
Subject: Inconsistent run times
Date: Tue, 30 Oct 2012 14:34:06 -0400

I am running glpk 4.44 downloaded from sourgeforge for 64-bit windows
I am writing a problem formulation to an LP file and then reading it 
into glpsol and also read it from my compiled program.
I am using Visual Studio 2010 to compile my 64-bit program.
I have observed the following inconsistencies

The first time a problem is imported and solved (it is a mip 
formulation) it runs about as fast as using glpsol.
The following times, the run times are 10 to 12 times LONGER (e.g. 1.2 
seconds first time, 14.2 seconds thereafter)
In my program I am timing only the mipopt call, not reading the lp file.

Sequence of calls

create problem
read lp file
mipopt with presolve
destroy problem

repeat the above sequence

The problem is destroyed and the corresponding glpk pointer is null 
between iterations.
However the glpk library is not unloaded between repeats of this sequence
When my program is restarted the sequence of events repeats, i.e. only 
the first time are the run times short.

Formulation is ultimately solved and no error codes are return (i.e. 
solution is reported as primal optimal which it is)

I have repeated this behavior on several different Windows 7 machines.









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