[Scip] Determinism

[Alejandro Burzyn]

Ok, thank you again, recently I've found what the difference was between the runs: I had changed the SCIP version from 1.1 to 1.2.
In the attach I've put the lp problem, and the stats of the runs of both versions of scip 
(precompiled binary for windows with soplex in both cases, default settings). The runs were made on an athlon xp 1.8 ghz, with 1 gb ram. 
I think the principal difference is in the root cuts, but I don't know if I should keep with 1.1 
or tune 1.2 a little. I'll be grateful for any advice.
Thank you very much,
Alejandro



--- El lun 19-oct-09, Tobias Achterberg <achterberg at zib.de> escribió:

De: Tobias Achterberg <achterberg at zib.de>
Asunto: Re: [Scip] Determinism
A: "Alejandro Burzyn" <aleburzyn at yahoo.com>
Cc: scip at zib.de
Fecha: lunes, 19 octubre, 2009, 6:30 am



Alejandro Burzyn wrote:
> Thank you all for your answers, I think I've made a mistake somewhere
> with the lp
> (I think I've modified it somewhere between runs). However, I did test
> on different computers
> with same lp and same binary, and there I saw differences in stats no
> related to time, is this behaviour expected?

Yes, if you run SCIP on different machines or on different operating systems, you will
most likely see differences in the solving process.

The reason is that many decisions in a mathematical programming solver are based on the
results of floating point arithmetic calculations. Since there are small differences
across machines and compilers on how to deal with round-off in floating point
calculations, the decisions are affected by machine type, compiler, and also compiler
options. In particular for MIP, a small difference in some decision can lead to a very
large difference in solving behavior.


Tobias



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