Why does interpolate not work with multiples of functions?

Question

from dolfin import *
mesh = UnitSquareMesh(2,2)
V = FunctionSpace(mesh, "CG", 1)
f = Function(V)
e = Function(V)

f.interpolate(e)
f.interpolate(2*e)

The first interpolate works but the second one doesn't. Shouldn't this be possible in dolfin? All interpolate has to do is to evaluate 2*e for the dofs of f.

Answer 1

The problem is that 2*e is an ufl.algebra.Product object (use type(2*e)) and the interpolate function only receive as argument a GenericFunction.

Consider:

f.interpolate(e)
e.vector()[:] *= 2
f.interpolate(e)

or

f.interpolate(e)
f.vector()[:] *= 2