Speed up initialization of MG transfer matrices by using a CompressedSimpleSparsityPa...

git-svn-id: https://svn.dealii.org/trunk@24172 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/source/multigrid/mg_transfer_prebuilt.cc b/deal.II/source/multigrid/mg_transfer_prebuilt.cc
index 951f1b7342a2b82838e963efcccc6e894656961e..56de732bc75905873d72156be916c6d7b1e3160e 100644 (file)
--- a/deal.II/source/multigrid/mg_transfer_prebuilt.cc
+++ b/deal.II/source/multigrid/mg_transfer_prebuilt.cc
@@ -18,6 +18,7 @@
 #include <deal.II/lac/block_vector.h>
 #include <deal.II/lac/sparse_matrix.h>
 #include <deal.II/lac/block_sparse_matrix.h>
+#include <deal.II/lac/compressed_simple_sparsity_pattern.h>
 #include <deal.II/grid/tria.h>
 #include <deal.II/grid/tria_iterator.h>
 #include <deal.II/dofs/dof_tools.h>
@@ -200,10 +201,9 @@ void MGTransferPrebuilt<VECTOR>::build_matrices (
                                       // increment dofs_per_cell
                                       // since a useless diagonal
                                       // element will be stored
-      prolongation_sparsities[level]->reinit (sizes[level+1],
-                                             sizes[level],
-                                             dofs_per_cell+1);
-
+      CompressedSimpleSparsityPattern csp (sizes[level+1],
+                                          sizes[level]);
+      std::vector<unsigned int> entries (dofs_per_cell);
       for (typename MGDoFHandler<dim,spacedim>::cell_iterator cell=mg_dof.begin(level);
           cell != mg_dof.end(level); ++cell)
        if (cell->has_children())
@@ -229,15 +229,19 @@ void MGTransferPrebuilt<VECTOR>::build_matrices (
                                                 // matrix which will be used
                                                 // for this pair of parent/child
                for (unsigned int i=0; i<dofs_per_cell; ++i)
-                 for (unsigned int j=0; j<dofs_per_cell; ++j)
-                   if (prolongation(i,j) != 0)
-                     prolongation_sparsities[level]->add (dof_indices_child[i],
-                                                          dof_indices_parent[j]);
+                 {
+                   entries.resize(0);
+                   for (unsigned int j=0; j<dofs_per_cell; ++j)
+                     if (prolongation(i,j) != 0)
+                       entries.push_back (dof_indices_parent[j]);
+                   csp.add_entries (dof_indices_child[i],
+                                    entries.begin(), entries.end());
+                 }
              }
          }
 
-      prolongation_sparsities[level]->compress ();
-
+      prolongation_sparsities[level]->copy_from (csp);
+      csp.reinit(0,0);
       prolongation_matrices[level]->reinit (*prolongation_sparsities[level]);
 
                                       // now actually build the matrices