From: Wolfgang Bangerth Date: Mon, 12 Aug 2019 23:54:09 +0000 (-0600) Subject: Update the description in step-8 that uses the new pictures. X-Git-Tag: v9.2.0-rc1~1248^2 X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F8557%2Fhead;p=dealii.git Update the description in step-8 that uses the new pictures. --- diff --git a/examples/step-8/doc/results.dox b/examples/step-8/doc/results.dox index 3179c1a22a..5171fee9e5 100644 --- a/examples/step-8/doc/results.dox +++ b/examples/step-8/doc/results.dox @@ -19,14 +19,10 @@ the $x$- and $y$-displacements as scalar components: You can clearly see the sources of $x$-displacement around $x=0.5$ and -$x=-0.5$, and of $y$-displacement at the origin. The next image shows the -final grid after eight steps of refinement: - - - +$x=-0.5$, and of $y$-displacement at the origin. What one frequently would like to do is to show the displacement as a vector -field, i.e., show vectors that for each point show the direction and magnitude +field, i.e., vectors that for each point illustrate the direction and magnitude of displacement. Unfortunately, that's a bit more involved. To understand why this is so, remember that we have just defined our finite element as a collection of two components (in dim=2 dimensions). Nowhere have @@ -34,15 +30,16 @@ we said that this is not just a pressure and a concentration (two scalar quantities) but that the two components actually are the parts of a vector-valued quantity, namely the displacement. Absent this knowledge, the DataOut class assumes that all individual variables we print are separate -scalars, and Visit then faithfully assumes that this is indeed what it is. In +scalars, and Visit and Paraview then faithfully assume that this is indeed what it is. In other words, once we have written the data as scalars, there is nothing in -Visit that allows us to paste these two scalar fields back together as a +these programs that allows us to paste these two scalar fields back together as a vector field. Where we would have to attack this problem is at the root, namely in ElasticProblem::output_results(). We won't do so here but instead refer the reader to the step-22 program where we show how to do this for a more general situation. That said, we couldn't help generating the data anyway that would show how this would look if implemented as discussed in -step-22. The vector field then looks like this (Visit randomly selects a few +step-22. The vector field then looks like this (Visit and Paraview +randomly select a few hundred vertices from which to draw the vectors; drawing them from each individual vertex would make the picture unreadable):