From: wolf Date: Wed, 7 Apr 1999 15:00:56 +0000 (+0000) Subject: Add comment about temporary vectors to doc. X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=16eb523707cbbe826446c34629a5c6243a1595cc;p=dealii-svn.git Add comment about temporary vectors to doc. git-svn-id: https://svn.dealii.org/trunk@1075 0785d39b-7218-0410-832d-ea1e28bc413d --- diff --git a/deal.II/lac/include/lac/solver_gmres.h b/deal.II/lac/include/lac/solver_gmres.h index 6535abf165..1f2536164c 100644 --- a/deal.II/lac/include/lac/solver_gmres.h +++ b/deal.II/lac/include/lac/solver_gmres.h @@ -27,6 +27,17 @@ * the number of iterations before a restart occurs is less by three than * the total number of temporary vectors. * + * Note that restarts don't compensate temporary vectors very well, i.e. + * giving too few temporary vectors will increase the necessary iteration + * steps greatly; it is not uncommon that you will need more iterations + * than there are degrees of freedom in your solution vector, if the number + * of temporary vectors is lower than the size of the vector, even though + * GMRES is an exact solver if a sufficient number of temporary vectors is + * given. You should therefore always give as many temporary vectors as you + * can, unless you are limited by the available memory; only then should you + * start to trade computational speed against memory. One of the few other + * possibilities is to use a good preconditioner. + * * @author Original implementation by the DEAL authors; adapted, cleaned and documented by Wolfgang Bangerth */ template