[!232] [!230] [bugfix] Use submatrix index vector to implement O(1) look-up

Merge branch 'cherry-pick-0f4b78a9' into 'releases/2.6'

ref:core/dune-istl Merge branch 'feature/fix-quadratic-umfpacksetup' into
'master'

ref:core/dune-istl Looking up if a column index is contained in submatrix
could degenerate to accumulated O(n) complexity for each row in the old
implementation. By setting up a look-up before, this can be improved to O(1).
Fortunately such a vector is constructed anyway so we can simple use it after
minor reordering of code.

This should fix [[#54]].

See merge request [[!230]]

Closes [#54]

(cherry picked from commit 0f4b78a9)

22a5ae5f \[bugfix\] Use submatrix index vector to implement O(1) look-up

See merge request [!232]

  [#54]: gitlab.dune-project.org/NoneNone/issues/54
  [!230]: gitlab.dune-project.org/core/dune-istl/merge_requests/230
  [!232]: gitlab.dune-project.org/core/dune-istl/merge_requests/232

dune/istl/colcompmatrix.hh

@@ -266,8 +266,11 @@ namespace Dune
     template<typename Iter>
     void addRowNnz(const Iter& row) const;
 
-    template<typename Iter, typename Set>
-    void addRowNnz(const Iter& row, const Set& s) const;
+    template<typename Iter, typename FullMatrixIndex>
+    void addRowNnz(const Iter& row, const std::set<FullMatrixIndex>& indices) const;
+
+    template<typename Iter, typename SubMatrixIndex>
+    void addRowNnz(const Iter& row, const std::vector<SubMatrixIndex>& indices) const;
 
     void allocate();
 
@@ -323,12 +326,12 @@ namespace Dune
   }
 
   template<class T, class A, int n, int m>
-  template<typename Iter, typename Map>
+  template<typename Iter, typename FullMatrixIndex>
   void ColCompMatrixInitializer<BCRSMatrix<FieldMatrix<T,n,m>,A> >::addRowNnz(const Iter& row,
-                                                                            const Map& indices) const
+                                                                            const std::set<FullMatrixIndex>& indices) const
   {
     typedef typename  Iter::value_type::const_iterator RIter;
-    typedef typename Map::const_iterator MIter;
+    typedef typename std::set<FullMatrixIndex>::const_iterator MIter;
     MIter siter =indices.begin();
     for(RIter entry=row->begin(); entry!=row->end(); ++entry)
     {
@@ -341,6 +344,17 @@ namespace Dune
     }
   }
 
+  template<class T, class A, int n, int m>
+  template<typename Iter, typename SubMatrixIndex>
+  void ColCompMatrixInitializer<BCRSMatrix<FieldMatrix<T,n,m>,A> >::addRowNnz(const Iter& row,
+                                                                            const std::vector<SubMatrixIndex>& indices) const
+  {
+    using RIter = typename Iter::value_type::const_iterator;
+    for(RIter entry=row->begin(); entry!=row->end(); ++entry)
+      if (indices[entry.index()]!=std::numeric_limits<SubMatrixIndex>::max())
+          ++mat->Nnz_;
+  }
+
   template<class T, class A, int n, int m>
   void ColCompMatrixInitializer<BCRSMatrix<FieldMatrix<T,n,m>,A> >::allocate()
   {
@@ -461,12 +475,6 @@ namespace Dune
     typedef typename std::iterator_traits<Iter>::value_type row_type;
     typedef typename row_type::const_iterator CIter;
 
-    // Calculate upper Bound for nonzeros
-    for(Iter row=mrs.begin(); row!= mrs.end(); ++row)
-      initializer.addRowNnz(row, mrs.rowIndexSet());
-
-    initializer.allocate();
-
     typedef typename MRS::Matrix::size_type size_type;
 
     // A vector containing the corresponding indices in
@@ -479,6 +487,12 @@ namespace Dune
     for(SIter index = mrs.rowIndexSet().begin(); index!=mrs.rowIndexSet().end(); ++index)
       subMatrixIndex[*index]=s++;
 
+    // Calculate upper Bound for nonzeros
+    for(Iter row=mrs.begin(); row!= mrs.end(); ++row)
+      initializer.addRowNnz(row, subMatrixIndex);
+
+    initializer.allocate();
+
     for(Iter row=mrs.begin(); row!= mrs.end(); ++row)
       for(CIter col=row->begin(); col != row->end(); ++col) {
         if(subMatrixIndex[col.index()]!=std::numeric_limits<size_type>::max())