From e8764441a73cc76ecc0e340adac1dca58e65f7d7 Mon Sep 17 00:00:00 2001
From: bangerth <bangerth@0785d39b-7218-0410-832d-ea1e28bc413d>
Date: Sun, 17 Mar 2013 16:02:54 +0000
Subject: [PATCH] Mention PETSc's optimized mode.

git-svn-id: https://svn.dealii.org/trunk@28922 0785d39b-7218-0410-832d-ea1e28bc413d
---
 deal.II/doc/external-libs/petsc.html | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/deal.II/doc/external-libs/petsc.html b/deal.II/doc/external-libs/petsc.html
index c9e8708c9f..ab786ce663 100644
--- a/deal.II/doc/external-libs/petsc.html
+++ b/deal.II/doc/external-libs/petsc.html
@@ -5,7 +5,7 @@
     <title>The deal.II Readme on interfacing to PETSc</title>
     <link href="../screen.css" rel="StyleSheet">
     <meta name="author" content="the deal.II authors <authors @ dealii.org>">
-    <meta name="copyright" content="Copyright (C) 2008, 2009, 2010, 2011, 2012 by the deal.II authors">
+    <meta name="copyright" content="Copyright (C) 2008, 2009, 2010, 2011, 2012, 2013 by the deal.II authors">
     <meta name="date" content="$Date$">
     <meta name="svn_id" content="$Id$">
     <meta name="keywords" content="deal.II">
@@ -47,7 +47,9 @@
       PETSc usually requires you to set the
       environment variables <code>PETSC_DIR</code> and <code>PETSC_ARCH</code>
       to a path to PETSc and denoting the architecture for which PETSc is
-      compiled. If these environment variables are set, then
+      compiled (a string you can choose however you like, it is simply
+      intended to identify one of possibly several different PETSc
+      installations). If these environment variables are set, then
       <acronym>deal.II</acronym> will pick them up during
       configuration, and store them. It will then also recognize that
       PETSc shall be used, and enable the wrapper classes.
@@ -129,6 +131,20 @@
       </pre>
     </p>
 
+    <p>
+      By default, PETSc is compiled in "debug mode". You can switch this to
+      "optimized mode" by adding the command line parameter
+      <pre>
+
+	--with-debugging=0
+      </pre>
+      to the call of <code>./config/configure.py</code> above. In some cases,
+      this has made linear solvers run up to 30% faster. As with choosing
+      between <acronym>deal.II</acronym>'s debug and optimized modes, you
+      should only use optimized PETSc builds once you have tested that your
+      program runs well in debug mode.
+    </p>
+
     <hr>
 
     <address>
-- 
2.39.5