# [Gmsh] Reflect mesh

Amit.Itagi at seagate.com Amit.Itagi at seagate.com
Wed Jan 31 17:47:42 CET 2007

```Hi,

Consider the following surface geometry ( I am working on a more involved
geometry. However, to explain the problem I am facing, the following
geometry is good enough.)

- - - - - - - - - -           - - - - - - - - - -
|                     |         |                       |
|                     |_ _ _|                       |
|                                                       |
|                                                       |
- - - - - - - - - - - - - - - - - - - - - - - - -

I need to apply a boundary condition connecting the left boundary to the
right ( eg: Periodic boundary condition). After searching the mailing list,
I found that the two boundaries need to have one to one correspondence in
terms of the points/edges. One way to do this is to make the two surfaces
transfinite. However, in my problem, the points at the top and the points
at the bottom have different characteristic length. Thus, when I mesh the
geometry with triangles, I have a gradient in the triangle size from top to
bottom. Thus, I end up with skewed/divided triangles near the boundary (
Ideally, I would like the transfinite points to be spaced with the same
progression as the characterictic size of the triangles).  My questions
follow:

1) What progression does the interpolation of characteristic length  follow
from top to bottom ? If I know this, I can use the same progression for the
transfinite points.

2) Another way is, not to make the lines transfinite, and hope to use the
mirror symmetry of the problem. I know that I can create the geometry using
a symmetry transformation. But is there a way to mesh one half and use the
mirror symmetry to generate the mesh for the mirrored half ?

Thanks

Rgds,
Amit

```