PostProcessManager.export_to_vtk cannot handle time-dependent additional functions

[e-moral-sanchez]

The method export_to_vtk of the class PostProcessManager accepts the arguments additional_logical_functions and additional_physical_functions that can be used for instance to pass the exact solution and plot the error.

However, at the moment this feature can only be used with time-independent simulations (static fields).

In the case of a time-dependent simulation, it should be possible to pass the argument:
additional_physical_functions={'exact_solution': lambda ti: lambdify(Omega.coordinates, solution(ti), modules='numpy')}