[Scip] Gurobi LP interface

[Marc Pfetsch]

Hi Eamonn,

the Gurobi-Interface in SCIP is not really working and I strongly 
recommend to currently not use it. The main point is that Gurobi 
currently does not offer access to some important functionality, e.g., 
some basis information which is heavily used in SCIP. As a consequence I 
doubt that SCIP with Gurobi can currently be as fast (or faster) than 
other LP-solvers (although I do not have empirical information). I hope 
that Gurobi in the future will allow access to the required 
functionality. Another consequence is that because of this I have lost 
interest in the Interface, so it is not really well maintained.

So my current recommendation for you would be to use another LP-solver.

In any case, I will have a look into the problems you describe.

Maybe you can answer the following questions off the list:

Can you send me an example where this happens or are you creating the 
constraints on your own? Which version of Gurobi are you using?

Note that some solvers need to split up ranged rows in any case, which 
is usually done automatically.

Best,

Marc



Eamonn Coughlan schrieb:
> Hi all,
> 
> I've been using SCIP for a few different projects, and recently tried switching
> from CPLEX and soplex to gurobi as an LP solver.
> The following problem occurs: "ERROR: Gurobi cannot handle ranged rows.".
> Some examination shows that this means any linear constraint with lhs < rhs.
> I checked the gurobi docs and it appears there is a GRBaddrangeconstrs() call,
> which appears to add equality constraints though.
> What is the idiomatic way to deal with this?
> Do i have to rewrite all my constraints (this would mean dealing with extra 
> pricing variables depending on which solver i use, so i dislike this 
> solution), or is there an easier way?
> I noticed that constraints seem to be split as _lhs and _rhs automatically 
> when i output my problem in LP format, so is there a way to get to these?
> Or is there a plan to support these in lpi_grb	.c in the future?
> I'd be willing to try this myself if there is no compelling reason why it 
> can't be done there.
> 
> Regards,
> Eamonn Coughlan
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