[Gmsh] forcing a single element type on a 3D mesh.

[David Romero]

Hello Christophe,

First, thanks for a great piece of software!

I am having troubles creating a 3D mesh that results in a single element
type. I want a mesh that contains only tetrahedra, but somehow I end up
with some pyramids that cause troubles downstream (e.g. the FENICS/DOLFIN
library supports meshes with a single element type). The main problem is
that, depending on the mesh size I set using the Mesh.MeshSizeFactor, the
mesh ends up having only tets or mostly tets with a few pyramids.

The domain is a box with a few cylinders inside. Attached is a sketch of
the geometry. The cylinders are created by extruding a circle, with no
recombination. Attached is a sample GEO file, which I generate from pygmsh.
Attached is also a sample geo file, but I am afraid is a bit hard to
follow, because it is generated automatically by pygmsh, based on a python
program I wrote to automate the mesh generation for different cases. The
geo file also takes some time to run.

What algorithm type should I use (e.g. in the command line)?
What options should I set for Mesh.Algorithm and Mesh.Algorithm3D to make
sure I get only tets?

Thanks,
David
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