Is there any to check whether the MIP solver (SCIP) is actually warm starting ?

[Regista6]

Hello,

I am using the SetHint function ( std::vector<std::pair<const MPVariable*, double> > hint) to set the values of the decision variable as per the initial solution that I have.

I can't determine whether the solver is actually starting from this solution. Is there any way to check that?

Secondly, since I am warm starting, shouldn't the final objective value be at least equal to that of the initial solution?. This doesn't seem to be the case.

Using or-tools v9.3 on VS 2022.

[lperron]

apart from enabling the solver log, I have no ideas.

[Regista6]

Hi,

Actually, after writing the question, I thought of enabling the solver log but couldn't find any syntax (C++) for it in the documentation

How do I enable the solver log?

[lperron]

solver.EnableOutput() Laurent Perron | Operations Research | ***@***.*** | (33) 1 42 68 53 00 Le ven. 8 juil. 2022 à 10:45, watchdogs132 ***@***.***> a écrit :

…

Hi, Actually, after writing the question, I thought of enabling the solver log but couldn't find any syntax for it in the documentation <https://developers.google.com/optimization/mip/mip_var_array#complete_programs> How do I enable the solver log? — Reply to this email directly, view it on GitHub <#3375 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACUPL3PTI33VWPTLSFYV2JLVS7TC3ANCNFSM522J2W2Q> . You are receiving this because you commented.Message ID: <google/or-tools/repo-discussions/3375/comments/3106164 ***@***.*** com>

[gregy4]

What about export of your model from ortools to format accepted by scip like lp ? In case it works worse directly from scip, your hints work. In case their performance is same no hints are used.

[Regista6]

Hi,

I haven't tried that but upon turning on the solver log, I found that SCIP accepts my complete feasible solution (completesol heuristic) but is unable to improve the initial solution.

[gregy4]

It is maybe time to try another mip solver. Except commercial solvers I can recommend highs solver. It should be supported by ortools in future versions directly by highs team. So far you can check it via export to lp format.

[Regista6]

Thanks. Will try that.