assemble 0 vectors

[Nico Schlömer]

The code

from dolfin import *

mesh = UnitIntervalMesh(20)
V = FunctionSpace(mesh, 'CG', 1)

v = TestFunction(V)

f = zero() * v * dx
#f = 0 * v * dx
#f = 1 * v * dx

assemble(f)

fails to execute with

ufl.log.UFLException: Unable to extract common cell; missing cell definition in form or expression

if the form that is to be assembled is factually 0.

This are blueprints about this on launchpad, cf. https://blueprints.launchpad.net/ufl/+spec/annotate-zero-with-arguments https://blueprints.launchpad.net/dolfin/+spec/zero-form-righthand-side.

[Martin Sandve Alnæs]

The dolfin blueprint you mention is limited to the solve(a == 0) context.

The general issue is in ufl: https://blueprints.launchpad.net/ufl/+spec/annotate-zero-with-arguments

For the exact example code you present, a workaround is to replace 0 with Constant(0.0).

I'm closing this as it's not a dolfin bug. I'll transfer the ufl issues to bitbucket later in June, I'm quite overworked atm.

[Martin Sandve Alnæs]

This is a known ufl issue, not a dolfin issue.