From b15b36a7bd2b79ae06cd1c2fa8bb3a81b9b0fcae Mon Sep 17 00:00:00 2001
From: wolf <wolf@0785d39b-7218-0410-832d-ea1e28bc413d>
Date: Tue, 30 Mar 2004 14:33:04 +0000
Subject: [PATCH] Make sure begin() doesn't return an iterator into an empty
 row.

git-svn-id: https://svn.dealii.org/trunk@8915 0785d39b-7218-0410-832d-ea1e28bc413d
---
 deal.II/lac/include/lac/sparse_matrix.h | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/deal.II/lac/include/lac/sparse_matrix.h b/deal.II/lac/include/lac/sparse_matrix.h
index 329fbc98ed..8e85d86884 100644
--- a/deal.II/lac/include/lac/sparse_matrix.h
+++ b/deal.II/lac/include/lac/sparse_matrix.h
@@ -2020,7 +2020,16 @@ inline
 typename SparseMatrix<number>::const_iterator
 SparseMatrix<number>::begin () const
 {
-  return const_iterator(this, 0, 0);
+                                   // search for the first line with a nonzero
+                                   // number of entries
+  for (unsigned int r=0; r<n(); ++r)
+    if (cols->row_length(r) > 0)
+      return const_iterator(this, r, 0);
+
+                                   // alright, this matrix is completely
+                                   // empty. that's strange but ok. simply
+                                   // return the end() iterator
+  return end();
 }
 
 
@@ -2038,7 +2047,16 @@ inline
 typename SparseMatrix<number>::iterator
 SparseMatrix<number>::begin ()
 {
-  return iterator(this, 0, 0);
+                                   // search for the first line with a nonzero
+                                   // number of entries
+  for (unsigned int r=0; r<n(); ++r)
+    if (cols->row_length(r) > 0)
+      return iterator(this, r, 0);
+
+                                   // alright, this matrix is completely
+                                   // empty. that's strange but ok. simply
+                                   // return the end() iterator
+  return end();
 }
 
 
-- 
2.39.5