[SCIP] Different results between 8.0.3 and 8.1.0

[s schnug]

Hi,

from the perspective of the solver, it only matters to find an optimal
(objective) solution which is feasible (given some tolerances).
Which solution of those candidates is picked is not guaranteed (although
deterministic).

What you describe is completely natural!
Every single change (e.g. heuristic priority weights; new heuristics) might
lead to different result-vectors for many people (if we assume proven
optimal result-status with the same objective).

It's even worse: You might see different result-vectors by just changing
your operating-system or hardware in general (cannot give guarantees about
SCIP here).
The mailing-list contained an interesting
runs-different-during-simulation-in-valgrind example today!

See https://coral.ise.lehigh.edu/mip-2008/talks/danna.pdf for some
"related" background.

You should never assume result-vectors being stable across solutions (and
maybe OS/hardware).
Sometimes, there is some additional modelling possible, which can express
your expectation about those side-constraints (e.g.
lexicographic-ordering). But often this hurts.


Greetings,
Sascha

(not a SCIP dev; but a happy user)

Am Do., 1. Feb. 2024 um 13:19 Uhr schrieb Thiago NOVAES <
thiago.novaes at princeps.com>:

> Hello,
>
>
>
> The result of a MIP (1 binary, 0 integer, 0 implicit integer, 2751
> continuous, 2452 constraints) is different between versions 8.0.3 and
> 8.1.0. Difference only in the variables, not in the objective function.
>
> Looking at the release notes for 8.0.4 and 8.1.0 I didn't find anything
> that justified the difference.
>
>
>
> Could anyone help me understand this better? Is there no guarantee on
> variables between versions? I can share the .lp if it helps.
>
>
>
> Best regards,
>
> Thiago
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