construct only valid iterators

git-svn-id: https://svn.dealii.org/trunk@7672 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/lac/include/lac/sparse_matrix_ez.h b/deal.II/lac/include/lac/sparse_matrix_ez.h
index 1a7dfff8fc723bb6a182ecbca0849719a30234e3..1ce408f6aed5996795e74c694e2d9cf7fd0f5336 100644 (file)
--- a/deal.II/lac/include/lac/sparse_matrix_ez.h
+++ b/deal.II/lac/include/lac/sparse_matrix_ez.h
@@ -786,7 +786,7 @@ class SparseMatrixEZ : public Subscriptor
     
                                     /**
                                      * STL-like iterator with the
-                                     * first entry.
+                                     * first existing entry.
                                      */
     const_iterator begin () const;
 
@@ -797,12 +797,17 @@ class SparseMatrixEZ : public Subscriptor
     
                                     /**
                                      * STL-like iterator with the
-                                     * first entry of row @p{r}.
+                                     * first entry of row @p{r}. If
+                                     * this row is empty, the result
+                                     * is @p{end(r)}, which does NOT
+                                     * point into row @p{r}..
                                      */
     const_iterator begin (const unsigned int r) const;
 
                                     /**
-                                     * Final iterator of row @p{r}.
+                                     * Final iterator of row
+                                     * @p{r}. The result may be
+                                     * different from @p{end()}!
                                      */
     const_iterator end (const unsigned int r) const;
     
@@ -1166,7 +1171,31 @@ const_iterator(const SparseMatrixEZ<number> *matrix,
                const unsigned short          i)
                :
                accessor(matrix, r, i)
-{}
+{
+                                  // Finish if this is the end()
+  if (r==accessor.matrix->m() && i==0) return;
+
+                                  // Make sure we never construct an
+                                  // iterator pointing to a
+                                  // non-existing entry
+
+                                  // If the index points beyond the
+                                  // end of the row, try the next
+                                  // row.
+  if (accessor.a_index >= accessor.matrix->row_info[accessor.a_row].length)
+    {
+     do
+       {
+         ++accessor.a_row;
+       }
+                                     // Beware! If the next row is
+                                     // empty, iterate until a
+                                     // non-empty row is found or we
+                                     // hit the end of the matrix.
+      while (accessor.a_row < accessor.matrix->m()
+            && accessor.matrix->row_info[accessor.a_row].length == 0);
+    }
+}
 
 
 template <typename number>
@@ -1175,12 +1204,15 @@ typename SparseMatrixEZ<number>::const_iterator&
 SparseMatrixEZ<number>::const_iterator::operator++ ()
 {
   Assert (accessor.a_row < accessor.matrix->m(), ExcIteratorPastEnd());
-  
+
+                                  // Increment column index
   ++(accessor.a_index);
+                                  // If index exceeds number of
+                                  // entries in this row, proceed
+                                  // with next row.
   if (accessor.a_index >= accessor.matrix->row_info[accessor.a_row].length)
     {
       accessor.a_index = 0;
-
                                       // Do this loop to avoid
                                       // elements in empty rows
       do
@@ -1463,7 +1495,8 @@ inline
 typename SparseMatrixEZ<number>::const_iterator
 SparseMatrixEZ<number>::begin () const
 {
-  return const_iterator(this, 0, 0);
+  const_iterator result(this, 0, 0);
+  return result;
 }
 
 template <typename number>
@@ -1480,7 +1513,8 @@ typename SparseMatrixEZ<number>::const_iterator
 SparseMatrixEZ<number>::begin (const unsigned int r) const
 {
   Assert (r<m(), ExcIndexRange(r,0,m()));
-  return const_iterator(this, r, 0);
+  const_iterator result (this, r, 0);
+  return result;
 }
 
 template <typename number>
@@ -1489,19 +1523,7 @@ typename SparseMatrixEZ<number>::const_iterator
 SparseMatrixEZ<number>::end (const unsigned int r) const
 {
   Assert (r<m(), ExcIndexRange(r,0,m()));
-
-                                  // Usually, we should return the
-                                  // first element of the next row.
   const_iterator result(this, r+1, 0);
-
-                                  // If r was the last row, this is
-                                  // always true. Otherwise, we have
-                                  // to make sure that there IS an
-                                  // entry in the next row. If not,
-                                  // we advance to the next valid
-                                  // entry or end().
-  if (r+1 < row_info.size() && row_info[r+1].length == 0)
-    ++result;
   return result;
 }