]> https://gitweb.dealii.org/ - dealii-svn.git/commitdiff
Add comment about temporary vectors to doc.
authorwolf <wolf@0785d39b-7218-0410-832d-ea1e28bc413d>
Wed, 7 Apr 1999 15:00:56 +0000 (15:00 +0000)
committerwolf <wolf@0785d39b-7218-0410-832d-ea1e28bc413d>
Wed, 7 Apr 1999 15:00:56 +0000 (15:00 +0000)
git-svn-id: https://svn.dealii.org/trunk@1075 0785d39b-7218-0410-832d-ea1e28bc413d

deal.II/lac/include/lac/solver_gmres.h

index 6535abf165aeeefe6c9677e1b9e3de583cb86f97..1f2536164c81b62cce42a7fc2a5b81b317b8ecdc 100644 (file)
  * 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<class Matrix, class Vector>

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