UFL expand_derivatives/indices fail with conditional in FEniCS dev

[Marie Elisabeth Rognes]

The below example fails with "ufl.log.UFLException: Component size mismatch." in FEniCS dev. Does not fail with 1.6

from dolfin import *
from ufl.algorithms import expand_derivatives, expand_indices

mesh = UnitSquareMesh(2, 2)
V = VectorFunctionSpace(mesh, "CG", 1, dim=5)
v = Function(V)
V = v[0]
a = grad(conditional(lt(V, -40), exp(-V), 0))[0]*dx
print a
expand_indices(expand_derivatives(a))

[Marie Elisabeth Rognes]

UFL only example for easier debugging

from ufl import *
from ufl.algorithms import expand_derivatives, expand_indices

Q = FiniteElement("CG", triangle, 1)
V = Coefficient(Q)
a = grad(conditional(lt(V, -40), V, 0.0))[0]
print "a = ", a
b = expand_derivatives(a)
print "b = ", b
c = expand_indices(b)
print "c = ", c

[Marie Elisabeth Rognes]

The (temporary) solution is of course:

import ufl
ufl.algorithms.apply_derivatives.CONDITIONAL_WORKAROUND = True

cf

commit ae59864654596d2e3aa4c7c5067bdd57e8b62a4e
Author: Martin Sandve Alnæs <[e-mail]>
Date:   Thu Mar 3 08:15:01 2016 +0100

    Make the bugfix in conditional derivatives to avoid inf/nan values in
    generated code default behaviour. This bugfix may break ffc if uflacs
    representation is not used, and if you hit this issue the old
    workaround in ufl can be enabled by setting

    ufl.algorithms.apply_derivatives.CONDITIONAL_WORKAROUND = True

    at the top of your fenics program.

[Martin Sandve Alnæs]

Removing milestone: 1.8 (automated comment)