ERROR:bad index

[raulgarcia66]

Hello,

I am using MibS with SYMPHONY to solve the attached problem (with index-based auxiliary file)
Test_4_Classes_mps-file.txt
Test_4_Classes_index-based-aux.txt
After about 25 minutes I get the following error:

ERROR:bad index
from function vector
from class CoinPackedMatrix

I was wondering if it had anything to do with numerical stability, considering these are very large problems.

A second issue is that the problem isn't properly read when using the name-based auxiliary file. All variables and constraints are understood to be part of the leader problem. I've tried combinations of @CONSTRSBEGIN, @CONSTRBEGIN, @CONSTSBEGIN, etc, in case it is to do with the exact keyword, but have not had success.
Test_4_Classes_name-based-aux.txt

Kind regards,
Raul

[tkralphs]

Hi @raulgarcia66 thanks for the report, we will see what we can figure out. @yuxies, can you take a look?

[yuxies]

Hi @raulgarcia66,

Could you let us know which MibS version you’re using?
If you built from the source, the commit ID would also help.

[raulgarcia66]

Hi @yuxies,

I am using version 1.6.1.
I built MibS on Sep 16, 2025 so I believe the commit ID would be 64ddc2e.

Thanks.

[yuxies]

Hi @raulgarcia66,

Thank you for the version info and sharing both versions of aux files.

1. About the ERROR:bad index

I wasn’t able to hit the exact same runtime error, but when checking with a debug build, an assertion triggers earlier while reading the problem data. This points to an indexing issue in the index-based auxiliary file: the lower row index is starting from 1, while MibS expects row numbering to start from 0 (the first row that isn't an N type). Starting from 1 causes an extra row to be kept internally, which later leads to a size mismatch and may eventually result in the CoinPackedMatrix “bad index” error you observed.

If you change the row numbering to be 0-based, this part should be resolved.

2. About the name-based auxiliary file

While checking this, I noticed there is a typo in our documentation on the Input File Format page. The correct constraints keywords should be:

• NUMCONSTRS
• CONSTRSBEGIN
• CONSTRSEND

These keywords apply to the released/stable version (stable/1.2).

I ran the model using your name-based auxiliary file with the keywords listed above, and the solve started normally and kept running without triggering the index error. I let it run for about 30 minutes as a quick check.

3. One more thing about the branch/version

Based on the commit ID, it looks like the build you are using may come from the master branch rather than a stable release. Some development versions use slightly different hard-coded keywords, which can affect how the name-based aux file is parsed. If so, I would suggest either:

• updating to the latest release if you installed via coinbrew interactive menu, or
• if building from source, making sure you are on the stable/1.2 branch.

Please let me know if switching the indexing and/or the stable branch resolves the issue on your side, or if you’re still seeing problems.