From: Wolfgang Bangerth Date: Wed, 14 Aug 2024 16:08:11 +0000 (-0600) Subject: Add a note to step-86. X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ae8739d0671acf34b4c7e317b02a21e4544bd972;p=dealii.git Add a note to step-86. --- diff --git a/examples/step-86/doc/results.dox b/examples/step-86/doc/results.dox index d578a0c659..b7b57f6f00 100644 --- a/examples/step-86/doc/results.dox +++ b/examples/step-86/doc/results.dox @@ -234,7 +234,14 @@ ourselves to blame for that by setting @code set match final time = false @endcode -in the input file. +in the input file. If hitting the end time exactly is important to us, +setting the flag to `true` resolves this issue. + +We can even reason why PETSc eventually chooses a time step of around +0.025: The boundary values undergo a complete cosine cycle within 0.5 +time units; we should expect that it takes around ten or twenty time +steps to resolve each period of a cycle to reasonable accuracy, and +this leads to the time step choice PETSc finds. Not all combinations of methods, time step adaptation algorithms, and other parameters are valid, but the main messages from the experiment