Adjoint of a form with TrialFunction & LinearSolver for a form with Function instead

[dokken]

@pa-beaufort

Btw, can you explain me when one should use TrialFunction and Function?
Or give me some reference explaining those (I haven’t found any yet).

See: fem.Function vs ufl.TrialFunctions - #2 by dokken

@pa-beaufort

Also, when should we use derivative(fun, var, trial) instead of derivative(fun, var)?

It depends on what you want to achieve.
The third argument is what is inserted as the perturbation variable after differentiation.