I believe you should do the following: beta = Constant(0.001) u = Function(Q) from ufl.mathfunctions import Exp alpha = Exp(beta*u) In this case alpha will be a UFL expression, which you can assemble into Function, or simply use it in a form. ________________________________ From: firedrake-bounces@imperial.ac.uk <firedrake-bounces@imperial.ac.uk> on behalf of Justin Chang <jychang48@gmail.com> Sent: 08 December 2015 22:38 To: firedrake Subject: [firedrake] Can a Function be used in an Expression? Hi all, As the title states, can a Function solution be used in an Expression? Say I have the following: beta = 0.001 u = Function(Q) alpha = Expression("exp(Beta*solution)",Beta=Betasolution=u) When I try to run this, I get an error saying "ValueError: setting an array element with a sequence". Am I not doing something correctly or is it simply not possible to do include u into an Expression? Thanks, Justin