From: wolf Date: Wed, 14 Apr 2004 22:00:07 +0000 (+0000) Subject: Add some more words. X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=357b37258e311b478d339291a1bd48a834a53f6b;p=dealii-svn.git Add some more words. git-svn-id: https://svn.dealii.org/trunk@9005 0785d39b-7218-0410-832d-ea1e28bc413d --- diff --git a/deal.II/doc/tutorial/chapter-2.step-by-step/step-15.data/intro.tex b/deal.II/doc/tutorial/chapter-2.step-by-step/step-15.data/intro.tex index 6544e05e15..a2a348177a 100644 --- a/deal.II/doc/tutorial/chapter-2.step-by-step/step-15.data/intro.tex +++ b/deal.II/doc/tutorial/chapter-2.step-by-step/step-15.data/intro.tex @@ -271,4 +271,26 @@ does not contain much new stuff, but if it explains a few of the techniques that are available for nonlinear problems and in particular 1d problems, then this is not so bad, after all. +\textbf{Note:} As shown below, the program starts the nonlinear solver from 10 different +initial values, and outputs the results. This is not actually too many, but we +did so to keep run-time short (around 1:30 minutes on my laptop). If you want to +increase the number of realizations, you may want to switch to optimized mode +(by setting the ``debug-mode'' flag in the Makefile to ``off''), and increase +the number of realizations to a larger value. On the same machine as above, I +can compute 100 realizations in optimized mode in about 2 minutes. For +this particular program, the difference between debug and optimized mode is +thus about a factor of 7-8, which can be explained by the fact that we ask the +compiler to do optimizations on the code only in the latter mode, but in most +part due to the fact that in optimized mode all the ``Assert'' checks are +thrown out that make sure that function arguments are correct, and that check +the internal consistency of the library. The library contains several +thousands of these checks, and they significantly slow down debug +computations, but we feel that the benefit of finding programming errors +earlier and including where the problem exactly appeared to be of signicantly +greater value than faster run-time. After all, all production runs of programs +should be done in optimized mode anyway. + +A slowdown of a factor of 7-8 is unusual, however. For 2d and 3d applications, +a typical value is around 4. + \end{document}