Re: Behaviour of compute_gradient

[Konstantinos Poulios]

Dear Eloi,

This function normally expects VD to have either the same Qdim as V.qdim() or 1. In your case, where V is a scalar MeshFem, the only option that I see for VD is to also be a scalar MeshFem.

BR

Kostas

On Wed, Jun 1, 2022 at 9:56 AM Eloi Martinet <eloi.martinet@univ-smb.fr> wrote:

Hello,

I'm using the python interface of GetFEM. I am a bit confused about the behaviour of the function compute_gradient. I would expect to use it the following way (for a planar 2D mesh) :

V = gf.MeshFem(mesh_2D, 1)
V.set_fem(gf.Fem("FEM_PK(2, 1)"))

VD = gf.MeshFem(V.linked_mesh(), 2)   # HERE
VD.set_fem(gf.Fem("FEM_PK_DISCONTINUOUS(2, 0)"))

f = some function over V

grad_f = gf.compute_gradient(V, f, VD)

However, when I do this, I have a Dimension mismatch, whereas there is no error when I put

VD = gf.MeshFem(V.linked_mesh(), 1)

even if grad_f is of size [2, VD.nbdof()] afterward.

Could you please explain this behaviour ? 

Sincerly yours,

Eloi MARTINET,

LJK, PhD Student.