Seeding CP-SAT solver

[Alberto Manzini]

Hi everyone, I was wondering if it is possible to set random search in CP-SAT solver more deterministic, like setting a random seed in the solver.

Thanks for help,

Alberto Manzini

[Laurent Perron]

Ok

 interleave_search:true,share_binary_clause:false, num_workers:16

Will start a deterministic search with 16 workers. 

It is usually way slower than the non deterministic version. 

--
You received this message because you are subscribed to the Google Groups "or-tools-discuss" group.
To unsubscribe from this group and stop receiving emails from it, send an email to or-tools-discu...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/or-tools-discuss/ae29896b-be79-4693-bb70-cbf4075cb0dfn%40googlegroups.com.

[Alberto Manzini]

Thanks for your reply, just another query: why set 16 as search workers? It's just to handle the fact solver will get slower to find solutions or it's somehow mandatory?

[Laurent Perron]

Single thread solve is already deterministic. 

I run my models with at least 16 workers. But you can set to whatever you want.

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

To view this discussion on the web visit https://groups.google.com/d/msgid/or-tools-discuss/a9ca47bc-2a84-4cf8-8b80-942bd5223f14n%40googlegroups.com.

[Frederic Didier]

When interleave_search is true, it does not matter as much.

You should just set it to your number of cores, what is important is the parameter "intearleave_batch_size".

Basically, to be deterministic, we split the solve into batch size independent chunks, wait for all of them to be solved by (num_workers), synchronize and generate the next batch.

So you usually want the batch size to be around twice the number of workers, so that you have a good utilization of your core if some chunks are fast to be completed.

For a fixed batch size, the result should be deterministic, independently of the number of workers.

To view this discussion on the web visit https://groups.google.com/d/msgid/or-tools-discuss/CABcmEeZNTZ9vSM%2BEkYzb8s0LvAsd3LbDa7jwxcBSQXEfdTCfoQ%40mail.gmail.com.

[Alberto Manzini]

Understood, thank you very much.

[Alberto Manzini]

I've set these parameters, but I'm not getting deterministic solutions yet. Am I missing something?

solver = cp_model.CpSolver()

solver. parameters.num_search_workers = self. num_search_workers

# set parameters to have deterministic saver search

solver.parameters.interleave_search = True

solver.parameters.interleave_batch_size = self. num_search_workers * 2

solver. parameters. share_binary_clauses = False

solver.parameters.max_time_in_seconds = self.num_minutes_to_solve * 60 + 1

Il giorno mercoledì 25 ottobre 2023 alle 16:20:35 UTC+2 or-tools-discuss ha scritto:

I've set these parameters, but I'm not getting deterministic solutions yet. Am I missing something?

[Frederic Didier]

Make sure you have the latest version, and also that you build your model in a deterministic way (the fingerprint in the log should be the same).

Also, if you hit the time limit, then of course you might hit it sooner or later, so this part will not be deterministic.

If nothing works, can you send us the proto of your model so we can check on our side?

To view this discussion on the web visit https://groups.google.com/d/msgid/or-tools-discuss/f60b1917-cafc-4a83-9077-4f5dd1c6d6fan%40googlegroups.com.