Hello, We have been following the documentation and examples to learn how to solve nonlinear problems in Firedrake. We want to solve the classical Fofonoff problem in a one-layer Quasi-Geostrophic problem. We have set up a nonlinear variational problem, following the Camassa-Holm demo. Unfortunately, whenever we try it we get an error saying that our for is not a linear form. Which is true, but since we are using NonlinearVariationalProblem, I presume this should be ok. Traceback (most recent call last): File "fofonoff_qg.py", line 41, in <module> psi_problem = NonlinearVariationalProblem(L, psi_soln, bcs=bc) File "/home/fpoulin/software/firedrake/src/firedrake/firedrake/variational_solver.py", line 47, in __init__ raise ValueError("Provided residual is not a linear form") ValueError: Provided residual is not a linear form Our code can be found on github. https://github.com/francispoulin/firedrakeQG/blob/master/fofonoff_qg.py If anyone has any advice or other examples that do this successfully, we would love to know more. Cheers, Francis ------------------ Francis Poulin Associate Professor Department of Applied Mathematics University of Waterloo email: fpoulin@uwaterloo.ca Web: https://uwaterloo.ca/poulin-research-group/ Telephone: +1 519 888 4567 x32637