[Scip] Adding model constraints after presolving

[Daniel Karch]

Never mind, I think I can implement this in a relaxation handler.

2011/12/16 Daniel Karch <karch at math.tu-berlin.de>

> Hi everyone,
>
> I have the following problem. I have an ILP formulation of a problem, it
> looks something like this:
>
> (P)
>
> min c'x
>
> Ax <= b
> Fx <= g
>
> x in {0,1}^n
>
> I would like to solve the following relaxation first,
>
> (P')
>
> min c'x
>
> Ax <= b
>
> x in {0,1}^n
>
> and then add the cuts in the system Fx <= g later (as linear constraints).
> The reason is that (P') is much faster so solve,
> I know that in this particular case the solution to (P') is probably a
> very good lower bound for the solution of (P),
> and I can also use it for a primal heuristic.
>
> The problem is now that the approach does not work as expected. I get told
> that the problem is infeasible and get:
>
> [src/scip/var.c:6341] ERROR: cannot change the bounds of a fixed variable
> [src/scip/var.c:6318] ERROR: Error <-9> in function call
> [src/scip/var.c:8079] ERROR: Error <-9> in function call
> [src/scip/prob.c:514] ERROR: Error <-9> in function call
> [src/scip/scip.c:7302] ERROR: Error <-9> in function call
> [src/scip/scip.c:7744] ERROR: Error <-9> in function call
> [src/scip/scip.c:4357] ERROR: Error <-9> in function call
> [src/scip/scip.c:586] ERROR: Error <-9> in function call
> [src/cppmain.cpp:107] ERROR: Error <-9> in function call
> SCIP Error (-9): method cannot be called with this type of data
>
> This does not occur if I disable presolving, so I guess that SCIP fixes
> some variables that it shouldn't.
> Is there some way to make SCIP "aware" of the constraints that I will
> eventually add, so that presolving
> does not destroy feasibility?
>
> Thanks
>
>   Daniel
>
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