[sfepy] Calculating strains from given nodal displacements

Hi! I have a tetrahedral mesh and know the nodal displacements of the mesh from an external software. I now want to calculate the element' strains and thought I give sfepy a go. However, the learning curve is very steep and I struggle a bit with this - I thought - easy task.

I thought I basically need this function here: https://sfepy.org/doc-devel/primer.html#post-processing but how do I initially setup the problem and set the already solved displacement vector?

This is what I got so far:

import numpy as np
from sfepy.discrete.fem import Mesh, FEDomain
from sfepy.discrete import Problem

# Given: mesh and nodal displacements
mesh = Mesh.from_file('the_mesh.vtk')
u_vec = np.random.random((mesh.n_nod, 3))  # here I would insert the 
actual displacements. Use random numbers for testing

domain = FEDomain('domain', mesh)
omega = domain.create_region('Omega', 'all')
# ???
pb = Problem('elasticity', domain=domain, ...)  # ???
# ???
strain = pb.evaluate('ev_cauchy_strain.2.Omega(u)', mode='el_avg')

Am I on the right track here? Thanks in advance!

Best, Sebastian