[Symphony] No feasible solution ..

[Ted Ralphs]

Sorry for the long delay in responding to this. When I run the models in
the most recent version of SYMPHONY, they are both found to be infeasible
in the presolve. If I turn off presolve, they are still both found
infeasible. I checked this with another solver and got the same result. So
I think your models are both infeasible.

This does not explain why you were getting different results with 5.6.1.
There were some bugs fixed in the preprocessor in some later releases so I
would first upgrade to the last release (5.6.11). Let me know if you have
more issues.

Cheers,

Ted

On Tue, Apr 21, 2015 at 4:10 AM, Mikko Alinikula - SUBNIC OY <
subnic at kolumbus.fi> wrote:

> Hello Ted,
>
> We have succeeded in making a truss-optimization-system using
> SYMPHONY-code in MILP-calculations.  Sometimes however SYMPHONY fails to
> find an optimum although it is there.   SYMPHONY claims that there are no
> feasible solutions when called with "find_first_feasible"-parameter.  I
> outputted .MPS-models of 2 cases :
>
> Attached is a .MPS-model, THERE_IS_NO_SOLUTION_FULL_MODEL.MPS, which is
> the original model.  SYMPHONY returns = NO FEASIBLE SOLUTIONS.
>
> Attached is a .MPS-model with, THERE_IS_A_SOLUTION_REDUCED_MODEL.MPS,
> which is the original model with reduced number of integer-variables.  For
> this SYMPHONY finds a optimum!  This is the optimum that is included also
> in the original model!
>
> SYMPHONY-version is currently 5.6.1 and OS is WIN 32/64.  I have linked
> statically SYMPHONY-libraries to my own code.
>
> Maybe some parameters for SYMPHONY needs to be adjusted? Or something ..
>
> BR
>
> Mikko Alinikula/SUBNIC Ltd./Finland
>
>
>
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>
>


-- 
Dr. Ted Ralphs
Professor, Lehigh University
(610) 628-1280
ted 'at' lehigh 'dot' edu
coral.ie.lehigh.edu/~ted
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