[Scip] Adding model constraints after presolving

[Daniel Karch]

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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