[SCIP] Warm starts and variable hints

[Antonia Chmiela]

Dear Marco,

thank you for your questions.

1. When you add a partial solution, it will always be stored right away, but solved later on (see Section 2.1.6 of the SCIP 4.0 release report: http://www.optimization-online.org/DB_FILE/2017/03/5895.pdf). To find out more information about how many solutions/incumbents were found by partial solutions, you need to look at the statistics of the heuristic „completesol“ in the log. The log can also tell you when completing a partial solution failed.   

2. No, SCIP does not have something similar to „var hint“.

I hope this answers all your questions.

Best,
Antonia

> Am 17.08.2021 um 15:29 schrieb Marco Correia <marco.v.correia at gmail.com>:
> 
> Hi all!
> 
> I have two questions:
> 
> 1. Is there a way to know if SCIP really made use of the warm start I'm passing? I'm currently doing something like this:
> 
> SCIPcreatePartialSol(p_env, &p_sol, NULL);
> SCIPsetSolVal(p_env, p_sol, p_scip_var, val)
> [repeat last line for all warm start variables]
> unsigned int stored;
> SCIPaddSolFree(p_env, &p_sol, &stored);
> if (!stored)
>     std::cout << "Warm start solution was ignored.\n";
> 
> It seems stored is always true, but it doesn't look like the warmstart is being helpful. Is there any way to know for sure?
> 
> 2. Gurobi has "var hint" feature where one can associate a value with a variable to guide search / improve heuristic. Is there anything like this in SCIP?
> 
> Thanks!
> Marco
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