Can't run VGM_for_Lorenz_attractor.py

[jpiabrantes]

Traceback (most recent call last):
  File "/home/joao/github/Variational_Gradient_Matching_for_Dynamical_Systems/VGM_for_Lorenz_attractor.py", line 125, in <module>
    state_couplings = find_state_couplings_in_odes(odes,symbols)
  File "./VGM_modules/import_odes.py", line 82, in find_state_couplings_in_odes
    membership = ismember(symbols.state,odes_sym[u].free_symbols)
AttributeError: 'function' object has no attribute 'free_symbols'

Would suggest adding a requirements.txt to the repo.