Difference in the objective value of a MIP in version 8.1.0

[Thiago-NovaesB]

files.zip

1. original.lp is a MIP problem.
2. permutation.lp is the same "original" problem but with permuted rows and columns.
3. table.png is a table with the objective value for each problem in each version.

When solving both problems in versions 8.0.3 and 8.0.4, I get exactly the same solution (default parameters). However, when solving with 8.1.0 I find totally different solutions.

In "original", the objective value is very similar, so it's not necessarily a problem. But "permutation" has a very different objective value.

Can you help me understand what is happening?

[DominikKamp]

Thanks for creating this issue!

Indeed, we already looked into your bug report and could reproduce a bug on original.lp. This is currently under investigation. We will let you know when there are more insights.

It could be traced back to an issue in PaPILO. So a possible workaround is to set presolving/milp/maxrounds = 0. Could you check if this leads to the same objective value on original.lp and permutation.lp in your setup?

[Thiago-NovaesB]

I found very close values, such as 71882637.3662884 and 71882637.3662881. The variables are very different.
It seems to me that this option really avoids the bug. I'll keep it that way until we have a more definitive solution.
Thanks!

[leoneifler]

I will close this issue for now, as we have a separate internal issue tracking the bug.

[DominikKamp]

This issue persists.