Hi, I have been trying to compute the gradient of scalar entity in c++ code. There is a relative example in python code in fenics book at page 20. To be more specific, i solved the laplace equation and i found the electric potential and now i want to compute the corresponding electric field. So I'm writing in ufl form:
helem = FiniteElement("Lagrange", tetrahedron, 1)
V_helem = VectorElement("Lagrange", tetrahedron, 1)
w = TrialFunction(V_helem)
v = TestFunction(V_helem)
u = Coefficient(helem)
a = inner(w,v)dx
L = -inner(nabla_grad(u),v)dx # Gradient of potential
where as coefficient u i put in my c++ code the computed electric potential. I run the program and as a result i take:
*** Error: Unable to assemble form.
*** Reason: Wrong type of function space for argument 0.
*** Where: This error was encountered inside Form.cpp.
*** Process: unknown
Does anyone have any idea how to accomplice this task??
Thank you
