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[Help-glpk] Different objective values

From: Joel Joel
Subject: [Help-glpk] Different objective values
Date: Thu, 17 Jul 2008 14:04:05 +0000 (GMT)


I am using GLPK to solve a problem by column generation.

I have a master problem "MP" which is a Mixed Integer Problem.

- STEP 1: the dual problem of the relaxed MP is solved iteratively and new columns are added at each iteration (the new columns are generated by solving a sub problem),
- STEP 2: the "MP" itself is solved (without relaxation).

I observe the LP objective value of the last iteration of STEP 1, and I noticed that it may change in the following situations:
1°) Using GLPK 4.27 compiled with GCC 4.3.0 and using GLPK 4.27 compiled with GCC 4.2.2,
2°) Using GLPK 4.27 compiled with GCC 4.2.2 and using GLPK 4.29 compiled with GCC 4.2.2.

-The objectives are the same using GLPK 4.27 and 4.29 both compiled with GCC 4.3.0,
-The column generator used is the same in all situations,
-The configuration of each compilation was:
 ./configure --enable-mysql=no --enable-iodbc=no --with-gmp

My questions are:
1°) Why do we have different objectives for the same problem,
2°) Is there an option / a way to obtain the same behavior in each situation?

Thanks in advance for your help &
Thanks for GLPK,


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