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. 

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