Originally posted by: MarioRuthmair

Hi!

When trying to solve the following model:

https://www.ads.tuwien.ac.at/~marior/model.tar.gz

using the interactive optimizer (x86-64_debian4.0_4.1 binary), CPLEX seems to hang when solving the root relaxation.

CPLEX> read problematic-model.lp
Problem 'problematic-model.lp' read.
Read time = 0.59 sec.
CPLEX> mipopt
Tried aggregator 1 time.
MIP Presolve eliminated 4546 rows and 4583 columns.
MIP Presolve modified 1947 coefficients.
Aggregator did 12 substitutions.
Reduced MIP has 126252 rows, 125981 columns, and 933417 nonzeros.
Reduced MIP has 125981 binaries, 0 generals, 0 SOSs, and 0 indicators.
Presolve time = 2.01 sec.
Clique table members: 5213.
MIP emphasis: balance optimality and feasibility.
MIP search method: dynamic search.
Parallel mode: deterministic, using up to 4 threads.

... here CPLEX hangs with full cpu load ...

I know this is a big model but similar models of same size can be solved rather quickly. Can anybody reproduce this hang?

Kind regards, Mario
#CPLEXOptimizers
#DecisionOptimization

Originally posted by: SystemAdmin

Can you please try

set mip display 4

before optimizing in the interactive? For me it does not hang but only makes very slow progress in the initial LP solve. The parameter setting above will give you more details about the simplex solve.
#CPLEXOptimizers
#DecisionOptimization

Originally posted by: MarioRuthmair

Thanks for the tip!

You are right, this does not seem to be a CPLEX bug but a completely degenerated model. Simplex needs about 10700 seconds to solve the LP relaxation which is quite slow for this number of rows and columns. Here is the log file:

https://www.ads.tuwien.ac.at/~marior/problematic-model.log

Maybe barrier or another LP method can help. I will try.
#CPLEXOptimizers
#DecisionOptimization