Allow to use UMFPackSolver as the base solver

Our polymorphic class hierarchy is flawed.  There is no real reason why the
MultigridStep class should be needed to be patched to accommodate for a new
base solver.  However, we are lacking a proper abstract interface for classes
that provide a 'setProblem' method.

dune/solvers/iterationsteps/multigridstep.cc

@@ -5,6 +5,7 @@
 
 #include <dune/solvers/transferoperators/multigridtransfer.hh>
 #include <dune/solvers/solvers/loopsolver.hh>
+#include <dune/solvers/solvers/umfpacksolver.hh>
 #include <dune/solvers/common/genericvectortools.hh>
 #include "blockgsstep.hh"
 
@@ -169,6 +170,9 @@ void MultigridStep<MatrixType, VectorType, BitVectorType>::preprocess()
         dynamic_cast<SmootherType*>(loopBaseSolver->iterationStep_)->ignoreNodes_ = ignoreNodesHierarchy_[0];
 
     }
+    // TODO: The following two #if-clauses do the exactly the same thing: the call setProblem
+    // However, we cannot write the code generically because there is no geral abstraction
+    // for solvers that I can call 'setProblem' for.
 #if HAVE_IPOPT
     else if (typeid(*this->basesolver_) == typeid(QuadraticIPOptSolver<MatrixType,VectorType>)) {
 
@@ -177,6 +181,15 @@ void MultigridStep<MatrixType, VectorType, BitVectorType>::preprocess()
         ipoptBaseSolver->setProblem(*(this->matrixHierarchy_[0]), *this->xHierarchy_[0], this->rhsHierarchy_[0]);
     }
 #endif
+#if HAVE_UMFPACK
+    else if (typeid(*this->basesolver_) == typeid(Dune::Solvers::UMFPackSolver<MatrixType,VectorType>)) {
+
+        Dune::Solvers::UMFPackSolver<MatrixType,VectorType>* umfpackBaseSolver
+            = dynamic_cast<Dune::Solvers::UMFPackSolver<MatrixType,VectorType>*> (this->basesolver_);
+
+        umfpackBaseSolver->setProblem(*(this->matrixHierarchy_[0]), *this->xHierarchy_[0], this->rhsHierarchy_[0]);
+    }
+#endif
 else {
         DUNE_THROW(SolverError, "You can't use " << typeid(*this->basesolver_).name()
                    << " as a base solver in a MultigridStep!");