[Scip] Infeasible results in scip, feasible in exported problem

Stefan Heinz heinz at zib.de
Fri Jan 29 14:43:26 MET 2010


Hi Matrin,

do you have a column generation problem?

Best Stefan

On Friday 29 January 2010 12:22:01 Martin Bergner wrote:
> Hello all,
> 
> I get infeasible solutions, again. This time, however, it is at least
> independent of the used LP solver.
> 
> I have a linear constraint \sum_i x_i = 1, the x_i \in [0, 1] are
> continuous but implicitly integer. It doesn't make a difference if I
> model them as such or as continuous. The integer value results from
> additional constraints which are not initial, but checked, propagated,
> separated and global. The explicit upper and lower bound is added to the
> variable.
> 
> The underlying problem is a routing problem where one path has to be
> chosen per order. The set partitioning constraint (modelled as linear
> because of the continuity) is the constraint enforcing this choice of
> exactly one order. After creating the problem with
> SCIPcreateVar/consLinear and adding the constraints and variables, I
> solve the problem. After solving, get the best solution with
> 
> SCIP_SOL* sol = SCIPgetBestSol(scip);
> 
> I get the value of my x variables with:
> 
> SCIPgetSolVal(scip, sol, model->getVariableX(i))
> 
> Now, I get various forms of infeasible solutions:
> 
> 1. more than 1 variable X of the order has value 1 (I checked the
> exported model, the set partitioning constraint is violated!)
> 
> 2. one or more of the X variables has a value > 1 (e.g. 5,6,7) which can
> not be feasible, as I explicitly set the upper bound of the created X
> variable to 1 (in SCIPcreateVar)
> 
> Solving the exported Model in cplex or scip provides the correct
> value ... .
> 
> This problem has appeared only recently but I don't know exactly when.
> Attached the exported model, which may not be of much benefit, since it
> is solved correctly after importing.
> 
> Regards,
> Martin
> 

-- 
Stefan Heinz

Zuse Institute Berlin (ZIB)
Takustr. 7
14195 Berlin
Germany

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