construction of Neumann data

Question

I have a Dirichlet problem: Laplace u =0 in Omega
u = f on partial Omega
defined in a mesh_dirichlet
and I will construct the Neumann data partial u/partail n =g
to define the Neumann problem:
Laplace u= 0 in Omega
partial u/partail n =g
in a mesh_Neumann

any help is appreciated for the reconstruction of g.

Answer 1

See section 1.1.13 of The FEniCS Book.