From: bangerth Date: Fri, 21 Mar 2008 21:00:29 +0000 (+0000) Subject: Comment on runtimes. X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ffd85ebdf71fee7d1b2e7f2f4d34a09dc729b74d;p=dealii-svn.git Comment on runtimes. git-svn-id: https://svn.dealii.org/trunk@15924 0785d39b-7218-0410-832d-ea1e28bc413d --- diff --git a/deal.II/examples/step-22/doc/results.dox b/deal.II/examples/step-22/doc/results.dox index 53888907d6..d324710ede 100644 --- a/deal.II/examples/step-22/doc/results.dox +++ b/deal.II/examples/step-22/doc/results.dox @@ -176,21 +176,18 @@ Refinement cycle 5 Assembling... Computing preconditioner... Solving... 14 outer CG Schur complement iterations for pressure. - -Refinement cycle 6 - Number of active cells: 170720 - Number of degrees of freedom: 4625150 (4432407+192743) - Assembling... - Computing preconditioner... - Solving... 15 outer CG Schur complement iterations for pressure. @endcode Again, we see that the number of outer iterations does not increase as we refine the mesh. Nevertheless, the compute time increases significantly: for each of the iterations above separately, it takes a -few seconds, a few seconds, 1min, 5min, 29min, 3h12min, and 21h39min -for the finest level with more than 4.5 million unknowns. This -superlinear (in the number of unknowns) increase is due to the fact +few seconds, a few seconds, 1min, 5min, 21min, and 1h35. (One level +more can be run on machines with more memory, though one may have to +replace the BlockCompressedSetSparsityPattern class by the +BlockCompressedSparsityPattern class as the former needs significantly +more memory and becomes the bottleneck; the latter class, however, has +a superlinear runtime complexity.) This overall +superlinear (in the number of unknowns) increase in runtime is due to the fact that our inner solver is not ${\cal O}(N)$: a simple experiment shows that as we keep refining the mesh, the average number of ILU-preconditioned CG iterations to invert the velocity-velocity block