[SCIP] Does SCIP use Ipopt as NLP local solver?

[Angel Manuel Gonzalez Rueda]

Thank you very much for the quick response Stefan.

So if we want to ensure to build scip with Ipopt, we must specify the flag
IPOPT=TRUE in the installation. But, the source code of the SCIPOptSuite
that we can download from the web:
[image: image.png]
Does also include the source code of Ipopt so it is immediately to do the
installation with it? Or does we need to install previously Ipopt from
other source?

Thank you very much,
Ángel


El sáb, 10 abr 2021 a las 11:11, Stefan Vigerske (<svigerske at gams.com>)
escribió:

> Hi,
>
> it depends on your build of SCIP whether you have included any or
> several NLP solvers. SCIP mentions early in the log which external codes
> it is linked with, so Ipopt would show up there if you have build SCIP
> with Ipopt.
>  From the 3 choices, Ipopt has highest priority, so you won't have to
> set nlp/solver.
>
> SCIP solves LP relaxations and runs primal heuristics. There are plenty
> of the latter that look for feasible solutions to the MIP relaxation (LP
> relaxation + integrality requirements). If such a solution is also
> feasible for the nonlinear constraints, then the upper bound is updated.
> The better the LP relaxation, the higher the chance that this happens.
> Having a NLP solver enables additional primal heuristics that explicitly
> take the nonlinear constraints into account, so the strength of the LP
> relaxation is less crucial for the upper bound.
>
> Stefan
>
> On 4/10/21 9:02 AM, Angel Manuel Gonzalez Rueda wrote:
> > Dear SCIP developers,
> >
> > I want to solve a Non-Linear Programming Problem with SCIP and I would
> like
> > to know what is the default Non-Linear Local solver that SCIP calls at
> each
> > step in order to obtain upper bounds during the branch and bound
> procedure.
> >
> > We have installed the SCIP Optimization Suite version 7.0.2 using the
> > source code for LINUX. It seems that by default the Ipopt solver is
> > installed (I am not sure about this), so I suppose that this is the one
> > that SCIP used by default.
> >
> > However, I have reviewed the list of all scip parameters, and I have
> found
> > the following parameter:
> > # solver to use for solving NLPs; leave empty to select NLPI with highest
> > priority
> > # [type: string, advanced: FALSE, default: ""]
> > nlp/solver = ""
> >
> > Thus, I do not have clear if it is mandatory to specify in this parameter
> > "Ipopt". Furthermore, in case Ipopt is not installed (even any NLPs
> > solver), how does SCIP to obtain upper bounds?
> >
> > Thank you in advance,
> > Ángel M. González Rueda
> >
> >
> > _______________________________________________
> > Scip mailing list
> > Scip at zib.de
> > https://listserv.zib.de/mailman/listinfo/scip
> >
>
>
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