OR-Tools v9.12: Use fixed intervals

[dop-amin]

This PR is based on #172.

According to a comment by Laurent Perron, this is supposed to improve efficiency of solving the constraint problem.

No thorough investigation about efficiency gains in our case has been done.

[mkannwischer]

@dop-amin, are you planning to investigate the performance impact of this, or what are we going to do with this PR?

[dop-amin]

I think using this feature of "newer" ortools versions is the right thing to do as it gives more information to the solver about the structure of the problem. I would think there is almost no way this could hurt the performance. I was waiting to investigate further until we've settled on a version of ortools back then. I don't have the time to follow up on the testing anymore.

Maybe it's enough to rebase this and roughly check CI times before merging.

[mkannwischer]

I think using this feature of "newer" ortools versions is the right thing to do as it gives more information to the solver about the structure of the problem. I would think there is almost no way this could hurt the performance. I was waiting to investigate further until we've settled on a version of ortools back then. I don't have the time to follow up on the testing anymore.

Maybe it's enough to rebase this and roughly check CI times before merging.

Sounds like a good plan to me. Can you rebase it, please?

[dop-amin]

I figured this feature seems to be new since 9.10(?) so merging now with 9.7 is incompatible.
We could leave this as a draft until we update the default or-tools version eventually or close for now and have an issue about this. I think keeping separate paths in the code for either would be a terrible thing to do.

[mkannwischer]

I figured this feature seems to be new since 9.10(?) so merging now with 9.7 is incompatible. We could leave this as a draft until we update the default or-tools version eventually or close for now and have an issue about this. I think keeping separate paths in the code for either would be a terrible thing to do.

Agreed - we should not have separete paths for different ortools versions.
We can just keep this open for now.