Clean up code

Compute coarse grid matrices in one loop only. This makes
the code a tiny bit cleaner and implies that a
coarse matrix is completely setup before being
used to setup the next coarser matrix.

This allows to construct the coarse matrix occupation
pattern depending on the fine matrix entries.

[[Imported from SVN: r6119]]

dune/solvers/iterationsteps/multigridstep.cc

@@ -55,9 +55,10 @@ void MultigridStep<MatrixType, VectorType, BitVectorType>::preprocess()
             DUNE_THROW(SolverError, "You have not supplied a multigrid restriction operator "
                        "for level " << i);
 
-    // The matrices for the linear correction problems
+    // /////////////////////////////////////////////////////
+    //   Assemble the complete hierarchy of matrices
+    // /////////////////////////////////////////////////////
     for (int i=this->numLevels_-2; i>=0; i--) {
-        
 
         // Delete coarse grid matrix if it exists already
         if (this->mat_[i]) {
@@ -66,21 +67,18 @@ void MultigridStep<MatrixType, VectorType, BitVectorType>::preprocess()
         }
 
         this->mat_[i] = new MatrixType;
-        
+
         // Compute which entries are present in the (sparse) coarse grid stiffness
         // matrices. 
         this->mgTransfer_[i]->galerkinRestrictSetOccupation(*this->mat_[i+1], *(const_cast<MatrixType*>(this->mat_[i])));
 
+        // setup matrix
+        this->mgTransfer_[i]->galerkinRestrict(*this->mat_[i+1], *(const_cast<MatrixType*>(this->mat_[i])));
+
         // Set solution vector sizes for the lower levels
         GenericVector::resize(this->x_[i],*this->mat_[i]);
     }
 
-    // /////////////////////////////////////////////////////
-    //   Assemble the complete hierarchy of matrices
-    // /////////////////////////////////////////////////////
-    for (int i=this->mgTransfer_.size()-1; i>=0; i--) 
-        this->mgTransfer_[i]->galerkinRestrict(*this->mat_[i+1], *(const_cast<MatrixType*>(this->mat_[i])));
-
     // /////////////////////////////////////////////////////
     //   Setup dirichlet bitfields
     // /////////////////////////////////////////////////////