> On 1 Jul 2019, at 13:29, Gib Bogle <[email protected]> wrote: > > I'm interested in knowing how the differences arise. I can understand how > different machines, compilers can give numerical results that differ at the > limits of the selected precision, but it's not obvious how this leads to the > generation of different meshes. >
Unstructured mesh generation is an iterative process, where adding a new mesh entity (e.g. a node) depends on the location of previous entities through geometrical calculations. It's thus very nonlinear, as a small perturbation on one node can lead to discrete decisions (e.g. swapping an edge) that will lead to substantially different final meshes. Christophe > Gib > From: gmsh <[email protected]> on behalf of moritz > braun <[email protected]> > Sent: Monday, 1 July 2019 10:28 p.m. > To: Christophe Geuzaine > Cc: [email protected]; [email protected] > Subject: [FORGED] Re: [Gmsh] Windows, Ubuntu give different meshes > > Dear Christophe > > I assume identical geometries leading to different meshes > between different versions of redhat 7.4 to 7.6 > can be expected. > I was quite surprised because my self consitent code behaved differently > depending > on the redhat version and now I understand! > > Regards > > Moritz > > > On Fri, Jun 28, 2019 at 8:04 AM Christophe Geuzaine <[email protected]> > wrote: > > > > On 27 Jun 2019, at 03:33, Gib Bogle <[email protected]> wrote: > > > > I have been testing with the demo file cube.geo: > > > > lc = 0.3; > > Point(1) = {0.0,0.0,0.0,lc}; > > Point(2) = {1,0.0,0.0,lc}; > > Point(3) = {1,1,0.0,lc}; > > Point(4) = {0,1,0.0,lc}; > > Line(1) = {4,3}; > > Line(2) = {3,2}; > > Line(3) = {2,1}; > > Line(4) = {1,4}; > > Line Loop(5) = {2,3,4,1}; > > Plane Surface(6) = {5}; > > tmp[] = Extrude {0,0.0,1} { > > Surface{6}; > > }; > > Physical Volume(1) = tmp[1]; > > > > I generate the mesh file at the command line like this: > > > > gmsh -3 cube.geo > > > > on a Windows 7 machine and on Ubuntu 16.04. The gmsh version is 4.3.0. > > > > I find that the meshes created on the two systems are a bit different. On > > Windows the mesh has 137 nodes and 372 elements, while on Ubuntu it has 136 > > nodes and 373 elements. > > > > Should I be concerned about this? > > No, on the same machine the meshes should be identical, but across OSes (and > different compilers) small variations are normal. > > Christophe > > > > > > Thanks > > Gib > > _______________________________________________ > > gmsh mailing list > > [email protected] > > http://onelab.info/mailman/listinfo/gmsh > > — > Prof. Christophe Geuzaine > University of Liege, Electrical Engineering and Computer Science > http://www.montefiore.ulg.ac.be/~geuzaine > > > > > _______________________________________________ > gmsh mailing list > [email protected] > http://onelab.info/mailman/listinfo/gmsh > > > -- > Prof M Braun Tel.:27-12-4298006/8027 > Physics Department Fax.: 27-12-4293643 > University of South Africa (UNISA) > [email protected] > P.O. Box 392 > 0003 > UNISA > South Africa > http://moritz-braun.blogspot.com > _______________________________________________ > gmsh mailing list > [email protected] > http://onelab.info/mailman/listinfo/gmsh — Prof. Christophe Geuzaine University of Liege, Electrical Engineering and Computer Science http://www.montefiore.ulg.ac.be/~geuzaine _______________________________________________ gmsh mailing list [email protected] http://onelab.info/mailman/listinfo/gmsh
