Dear Firedrakers, The attached code runs and gives good convergence for linear and quadratic DG basis. But when I run the scheme with a constant basis I get the following error: This integral is missing an integration domain. Traceback (most recent call last): File "compressible_acoustic.py", line 98, in <module> L1 = -div_u(dFdu_vec, dHdrho0) File "compressible_acoustic.py", line 94, in div_u return (dot(u, grad(p)))*dx + (jump(p)*dot((u('-')*(1-theta)+u('+')*theta), n('-')))*(dS) File "/usr/not-backed-up/firedrake/2016-05-11/firedrake/lib/python2.7/site-packages/ufl/measure.py", line 398, in __rmul__ error("This integral is missing an integration domain.") File "/usr/not-backed-up/firedrake/2016-05-11/firedrake/lib/python2.7/site-packages/ufl/log.py", line 158, in error raise self._exception_type(self._format_raw(*message)) ufl.log.UFLException: This integral is missing an integration domain. I've had a working version, including a constant basis, when I had the terms separately instead of being a definition. So I'm not quite sure where the error is. Regards, Will