]> https://gitweb.dealii.org/ - dealii-svn.git/commitdiff
Extend the docs a little more.
authorwolf <wolf@0785d39b-7218-0410-832d-ea1e28bc413d>
Mon, 15 Mar 2004 23:45:29 +0000 (23:45 +0000)
committerwolf <wolf@0785d39b-7218-0410-832d-ea1e28bc413d>
Mon, 15 Mar 2004 23:45:29 +0000 (23:45 +0000)
git-svn-id: https://svn.dealii.org/trunk@8760 0785d39b-7218-0410-832d-ea1e28bc413d

deal.II/lac/include/lac/sparsity_pattern.h

index 7e3d751e9732a20791c7487f9be3857df7827389..5c530be0d385d83918edca0632a5ddd5a00a4ea9 100644 (file)
@@ -742,23 +742,35 @@ class SparsityPattern : public Subscriptor
                                      * uses special convention for
                                      * quadratic matrices.
                                      *
-                                     * A return value <tt>true</tt>
-                                     * means that diagonal elements
-                                     * are stored first in each
-                                     * row. This is required by
-                                     * relaxation methods like
-                                     * Jacobi() and SOR(). A side
-                                     * effect of this scheme is that
-                                     * each row contains at least one
-                                     * element.
+                                     * A return value <tt>true</tt> means
+                                     * that diagonal elements are stored
+                                     * first in each row. A number of
+                                     * functions in this class and the
+                                     * library in general, for example
+                                     * relaxation methods like Jacobi() and
+                                     * SOR(), require this to make their
+                                     * operations more efficient, since they
+                                     * need to quickly access the diagonal
+                                     * elements and do not have to search for
+                                     * them if they are the first element of
+                                     * each row. A side effect of this scheme
+                                     * is that each row contains at least one
+                                     * element, even if the row is empty
+                                     * (i.e. the diagonal element exists, but
+                                     * has value zero).
                                      *
-                                     * A return value <tt>false</tt>
-                                     * means that diagonal elements
-                                     * are stored anywhere in the
-                                     * row. In particular, a row or
-                                     * even the whole matrix may be
-                                     * empty.
-                                    */
+                                     * A return value <tt>false</tt> means
+                                     * that diagonal elements are stored
+                                     * anywhere in the row, or not at all. In
+                                     * particular, a row or even the whole
+                                     * matrix may be empty. This can be used
+                                     * if you have block matrices where the
+                                     * off-diagonal blocks are quadratic but
+                                     * are never used for operations like the
+                                     * ones mentioned above. In this case,
+                                     * some memory can be saved by not using
+                                     * the diagonal storage optimization.
+                                      */
     bool optimize_diagonal () const;
     
                                      /**

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