[Bug-glpk] Bug with GLPK/glpkmex

[Ali Ozer Ercan]

Hi,

I am using GLPK with matlab (with the glpkmex extension) and I found a
bug. Please extract the attached tarball and run glpk_fail_example.m
in Matlab (you need glpkmex, the interface to Matlab). It is a simple
routing optimization. The first plot shows the possible links between
nodes and the numbers (in blue) on the links show the capacity in
Mbps. The flows are 18Mbps so the routes cannot use the links with
12Mbps capacity. This translates to an upper bound constraint in GLPK.
I solve the problem with both GLPK and Matlab's 'bintprog'. The
bintprog gives the right solution (last 3 plots) while the solution
given by GLPK (plots 2, 3 and 4) do use the links with 12 Mbps
capacity, which means the UB constaint is violated. This is also
detected by the lines 42--45 of solve_opt.m. The warning is executed
if the ub constraint is violated, and the exit status of glpk is 5.

I don't know if this is a problem of GLPK or glpkmex, but since
glpkmex is just a Matlab interface to GLPK and it is GLPK who is
performing the optimization, I thought this is probably GLPK's bug.

Best,

Ali Ercan.

-- 
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Ali Ozer Ercan
Post Doctoral Researcher
Berkeley Wireless Research Center
2108 Allston Way, Suite 200
Berkeley, CA 94704-1302 USA
http://www.eecs.berkeley.edu/~aliercan
+++++++++++++++++++++++++++++++++++

glpk_fail_example.tar.gz
Description: GNU Zip compressed data