Hello, We are trying to translate part of the mixed-poisson Fenics demo into Firedrake. I know that there is already a Firedrake demo that does this but for the special case of a square. I am hoping we can do this more generally. Below are the lines of code from Fenics. Can someone suggest how this could be implemented in Firedrake? Cheers, Francis https://fenics.readthedocs.io/projects/dolfin/en/latest/demos/mixed-poisson/... # Define function G such that G \cdot n = g class BoundarySource(Expression): def __init__(self, mesh, **kwargs): self.mesh = mesh def eval_cell(self, values, x, ufc_cell): cell = Cell(self.mesh, ufc_cell.index) n = cell.normal(ufc_cell.local_facet) g = sin(5*x[0]) values[0] = g*n[0] values[1] = g*n[1] def value_shape(self): return (2,) G = BoundarySource(mesh, degree=2) # Define essential boundary def boundary(x): return x[1] < DOLFIN_EPS or x[1] > 1.0 - DOLFIN_EPS bc = DirichletBC(W.sub(0), G, boundary) ------------------ Francis Poulin Associate Professor Department of Applied Mathematics University of Waterloo email: fpoulin@uwaterloo.ca Web: https://uwaterloo.ca/poulin-research-group/ Telephone: +1 519 888 4567 x32637