Restrict 3D vector for using it in dot() with a 2D grad

Question

I would like to form a dot product of the first two components of a three-dimenstional vector with grad(u) from a two-dimensional mesh. How can I select the components of conv such that the following code works?

from dolfin import *

mesh = UnitSquareMesh(10, 10)

V = FunctionSpace(mesh, 'CG', 1)

conv = Constant([1.0, 2.0, 3.0])  # comes from elsewhere

u = TrialFunction(V)
# ufl.log.UFLException: Dimension mismatch in dot product.
dot(conv, grad(u))

alexmm · Answer 1 · Jun 6, 2017

Best answer

I can't run this at the moment to check it but this might work:

conv2 = as_vector((conv[0], conv[1]))

dot(conv2, grad(u))

Source: https://media.readthedocs.org/pdf/fenics-ufl/latest/fenics-ufl.pdf

answered Jun 6, 2017 by alexmm FEniCS User (4,240 points)
selected Jun 6, 2017 by nschloe

It's missing brackets, but that does the trick. Thanks!

commented Jun 6, 2017 by nschloe FEniCS User (7,120 points)

I changed the answer to add the missing brackets. Is that what you used?

commented Jun 6, 2017 by alexmm FEniCS User (4,240 points)

Restrict 3D vector for using it in dot() with a 2D grad

1 Answer