FFC compilation fails for RT x Discontinuous Lagrange Trace

[Marie Elisabeth Rognes]

The below UFL code fails with the following error:

File "/home/meg/local/fenics/master/lib/python2.7/site-packages/FIAT/mixed.py", line 103, in tabulate arr[slice(ir), slice(cr)] = tab

ValueError: could not broadcast input array from shape (3,1,2) into shape (3,1,3)

# Define finite element spaces and mixed function space
S = FiniteElement("RT", triangle, 1)
V = FiniteElement("Discontinuous Lagrange Trace", triangle, 0)
M = MixedElement(S, V)
#M = FunctionSpace(mesh, MixedElement(S, V))

# Unknowns and test functions
s = TrialFunction(M)
phi = TestFunction(M)

# Define variational formulation (backward Euler)
a = inner(s[0], phi[0])*dx()

# Runs with old fenics dev Docker image labelled 2016.1.0dev
# Fails with current FFC master

[Miklós Homolya]

It seems that the issue is not in MixedElement but rather in HDivTrace, and the offending commit is 38751784 in FIAT. The following patch to FIAT seems to fix the issue:

diff --git a/FIAT/hdiv_trace.py b/FIAT/hdiv_trace.py
index 4e40019..a59e051 100644
--- a/FIAT/hdiv_trace.py
+++ b/FIAT/hdiv_trace.py
@@ -204,7 +204,7 @@ class HDivTrace(FiniteElement):
             # If not successful, return NaNs
             if not success:
                 for key in phivals:
-                    phivals[key] = np.full(shape=(sd, len(points)), fill_value=np.nan)
+                    phivals[key] = np.full(shape=(self.space_dimension(), len(points)), fill_value=np.nan)

                 return phivals

[Marie Elisabeth Rognes]

Thanks Miklos, that fixes the compilation error. Will you push this fix?

I'm still getting really non-satisfactory results for the complete test case however, possibly related to UFLACS, I'll find a new MWE.

[Miklós Homolya]

Pushed patch to next, will merge to master if it passes CI.

[Miklós Homolya]

Fixed in FIAT 6b54fb5.