[Gmsh] Problem in anisotropic mesh generation

[Andrea Ferrero]

Dear Gmsh users,
I am trying to generate anisotropic meshes by the BAMG tool included in 
Gmsh.
I can't get anisotropic elements when the elements  are oriented to 
certain directions.

For example, I generated an isotropic background mesh on a circular 
domain (radius=2) which I used to define a metric file. In each node of 
the this background mesh I define the metric tensor with the same 
parameters for all the nodes. In particular, I set h1=0.1, h2=0.5 and 
theta=pi/4. The obtained metric field shows the following parameters: 
m11=52, m22=52, m12=48.
If I use these parameters I get the required anisotropic mesh shown in 
the image aniso.png.

However, if I set theta=-pi/4 or theta=3*pi/4 I get the isotropic mesh 
reported in the image iso.png. I would expect to get an anisotropic mesh 
also with these parameters but with the elements aligned to a direction 
perpendicular to the previous case.
In this second case the parameters of the metric field are m11=52, 
m22=52, m12=-48.
Why do I get an isotropic mesh when theta=-pi/4?

I use the following command to generate the mesh with Gmsh 2.10.1:
gmsh -2 test.geo -algo bamg -bgm metric_file.mtr -anisoMax 100

Thank you very much

Andrea
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