[Scip] ZPL reader / Solution process deterministic?

[Moritz Drexl]

Hi Thorsten,
 
okay, I noticed that restarting scip between two runs makes the
solution process deterministic again. So maybe there is a bug with the
seeding of the random number generator.
 
Regards,
Moritz
 

>>> Thorsten Koch <koch at zib.de> 9/9/2010 8:44 >>>
Hi Moritz,

Am 09.09.2010 08:34, schrieb Moritz Drexl:
> Hi all and thanks for answering my last question!
>  
> I have two more questions:
>  
> 1) I noticed that when reading my zimpl files directly in scip (via
read file.zpl) the LPs get solved faster than with the indirect version
where I generate an .lp file first and then read it in scip (read
file.lp). What does the zimpl file reader do that zimpl itself doesn't
do (or vice versa)?

if you read the zimpl model directly, some rows or columns may be
permutated compared to the generated .lp file.
This can lead (depending on the model) to quite different solver runs.
This is known and to a certain degree
unavoidable.

> 
> 2) I was wondering whether the solution process of scip is
deterministic if all input and parameters are constant, or maybe if
there is some randomness involved in choosing heuristics/branching
rules/etc. If so, is there a way to make scip run deterministically?
> 
It should be deterministic if there are no bugs (uninitialized
variables) and the cpu behaves deterministic in the above sense.

Best regards,
Thorsten


> Regards,
> Moritz
> 
> 
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-- 
The important thing is not to stop questioning.
Curiosity has its own reason for existing.          -- Albert Einstein
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Dr. Thorsten Koch / Konrad-Zuse-Zentrum für Informationstechnik Berlin
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_______________/  DFG Research Center "Matheon"  http://www.matheon.de

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