[petsc-users] DMPlexCreateGmsh

Matthew Knepley knepley at gmail.com
Fri Jan 10 19:14:43 CST 2014

On Fri, Jan 10, 2014 at 3:44 PM, Dharmendar Reddy
<dharmareddy84 at gmail.com>wrote:

> Hello,
>         I have a question and feature request regarding DMPlexCreateGmsh.
> Gmsh, mesh format outputs, physical regions in the mesh as
> For example in the a particular 2 d mesh with eight physical regions
> it may look like the one below
> $PhysicalNames
> 8
> 1 1 "RegionName1"
> 1 2 "RegionName2"
> 1 3 "RegionName3"
> 2 4 "RegionName4"
> 2 5 "RegionName5"
> 2 6 "RegionName6"
> 2 7 "RegionName7"
> 2 8 "RegionName8"
> $EndPhysicalNames
> It would be nice to have the DMPLexCreateGmsh process this information.
> The first number in each row of name is the topological dimension (tdim),
> If the code can group all the regions with dimension < mesh dimension
> (meshDim) as "Boundary"  and all regions with dimension =
> meshDimension as "Region"
> Gmsh outputs (if requested) the lower dimension cells in regions with
> tdim  < meshDim. If interpolate mesh is enabled, i would like to have
> cells of boundary region, which in the above example will be lines and
> points, included in the boundary strata with global numbering for the
> facets.

I really hate GMsh right now. The format is a complete cluster of idiocy.
They allow
outputting facets as separate lower-dimensional cells, unconnected to the
cell, so we would have to initiate a search for every insertion. Not to
mention that sizes
are not declared up front so that we have to run through the file in
multiple passes. I
really really hate these guys. Is there an overwhelming reason to waste my
time messing
around with a format designed by the mentally infirm?

I am willing to listen to reason, but reading Gmsh files would make anyone
unreasonably angry.


> This ways the total number of Cells in the mesh will be : NumNodes +
> NumLines+ NumTriangles or NumNodes+ NumTriangles (if interpolate is
> off)
> In the Current implementation, correct me if i am wrong, I see the the
> total number of cells = numNodes + (some Lines which are elements of
> the lower dimensional regions) + numTriangles
> Thanks
> Reddy
> --

What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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