Hi everyone. I solving Poisson equation in 3d box and i would like to set Neumann boundary condition in every cell of exterior surface. I thought to use Raviart Thomas element but i dont know how to set these boundaries conditions. Any help would be much appreciated. Thank you !!!
You can consider the method used in this demo:
https://fenicsproject.org/docs/dolfin/latest/python/demos/neumann-poisson/demo_neumann-poisson.py.html