[bugfix] Allow different multi-index type for row and column

dune/fufem/assemblers/istlbackend.hh

@@ -221,17 +221,17 @@ public:
     return {*matrix_};
   }
 
-  template<class MultiIndex>
-  const Entry& operator()(const MultiIndex& row, const MultiIndex& col) const
+  template<class RowMultiIndex, class ColMultiIndex>
+  const Entry& operator()(const RowMultiIndex& row, const ColMultiIndex& col) const
   {
-    MatrixMultiIndexResolver<const Entry&, MultiIndex, MultiIndex> i(row, col);
+    MatrixMultiIndexResolver<const Entry&, RowMultiIndex, ColMultiIndex> i(row, col);
     return i(*matrix_);
   }
 
-  template<class MultiIndex>
-  Entry& operator()(const MultiIndex& row, const MultiIndex& col)
+  template<class RowMultiIndex, class ColMultiIndex>
+  Entry& operator()(const RowMultiIndex& row, const ColMultiIndex& col)
   {
-    MatrixMultiIndexResolver<Entry&, MultiIndex, MultiIndex> i(row, col);
+    MatrixMultiIndexResolver<Entry&, RowMultiIndex, ColMultiIndex> i(row, col);
     return i(*matrix_);
   }