Add some documentation.

git-svn-id: https://svn.dealii.org/trunk@5424 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/lac/include/lac/sparsity_pattern.h b/deal.II/lac/include/lac/sparsity_pattern.h
index 525b9c5da536a4db9fa262b0bb11c42fa7b2725d..0c16477b579857525009c66069263e7345d6d2a0 100644 (file)
--- a/deal.II/lac/include/lac/sparsity_pattern.h
+++ b/deal.II/lac/include/lac/sparsity_pattern.h
@@ -584,7 +584,20 @@ class SparsityPattern : public Subscriptor
                                     /**
                                      * Access to column number field.
                                      * Return the column number of
-                                     * the @p{index}th entry in @p{row}.
+                                     * the @p{index}th entry in
+                                     * @p{row}. Note that the if the
+                                     * matrix is square, then the
+                                     * first element in each row is
+                                     * the diagonal element,
+                                     * i.e. @p{column_number(row,0)==row}.
+                                     *
+                                     * If the sparsity pattern is
+                                     * already compressed, then
+                                     * (except for the diagonal
+                                     * element), the entries are
+                                     * sorted by columns,
+                                     * i.e. @p{column_number(row,i)}
+                                     * @p{<} @p{column_number(row,i+1)}.
                                      */
     unsigned int column_number (const unsigned int row,
                                const unsigned int index) const;