# Two questions on GMSH

**behzad tavassoli hozori**
tavassoli at hotmail.com

*Tue Jun 22 18:37:11 CEST 1999*

Dear Christophe Geuzaine,
I have downloaded GMSH which you have
kindly presented as public domain. It works
very well in Win NT. Unfortunately I have
had problems using GMSH efficiently in some
cases. Any help in these regards would be
deeply appreciated.
1) Involved in analyzing passive microwave
devices, I frequently encounter multimaterial
domains. However I have not succeeded in
defining such multiregions( multi-volumes)
in GMSH. For example consider a small box
of material A( with mesh density MDA) in a
larger box of material B( with mesh density
MDB). How can the user make GMSH mesh the two
regions (i.e. A &(B-A)) so that their meshes
would be consistent as regards to surface
meshes on the faces of A?
*******************
2) The second point is the way GMSH allows
the user to control the mesh density. Consider
a rectangular waveguide( box). How can the
user make GMSH create a graded mesh for the
box, with nearly minimum tetrahedrons, with
the following mesh density:
2-1) MDA for the internal points.
2-2) MDB for the points on two opposite
faces of the box, so that MDB>MDA.
This means any of the eight main vertices
of the box will be on one of the two mentioned
faces. For GMSH, this means the mesh density
will be equal to MDB everywhere in and on
( the faces of) the box. In other words, one
can not have the desired mesh density MDA for
the internal points. Is there any solution to
this case which does not require adding any
auxiliary points( with mesh density MDA).
This is the case when analyzing a multiport
waveguide network. As you might know, the mesh
density on the ports should be much more than
that of internal points.
*******************
I shall be looking forward to hearing
from you soon.
Behzad Tavassoli
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