Dear Firedrakers, Please excuse my excitement, but the expressions compiler is extremely cool. For example, it allows an application of an SSPRK timestepping scheme in the following compact form: while (t <= end): solve(lhsA == action(rhsA,oldT), newT) T1.assign(newT) solve(lhsA == action(rhsA,T1), newT) T2.assign(0.75*oldT + 0.25*newT) solve(lhsA == action(rhsA,T2), newT) newT.assign((1.0/3.0)*oldT + (2.0/3.0)*newT) oldT.assign(newT) cheers --cjc