Error on combine test or trial functions from different spaces

[dokken]

@VICTORIA_CHAN

(D) Norm of velocity coefficient vector (monolithic, direct): nan
(D) Norm of pressure coefficient vector (monolithic, direct): nan
Traceback (most recent call last):
  File "/Users/victoriachan/Documents/CityU Doc/FYP/python_files/ProgramV4.py", line 98, in <module>
    assert np.isclose(norm_u_3, norm_u_0)
NameError: name 'norm_u_0' is not defined. Did you mean: 'norm_u_3'?

Please look carefully at the demo, as norm_u_0 = u.x.norm() is defined in the code.

@VICTORIA_CHAN

Also, I am wondering from which part I can start to solve the problem to get its eigenvalue. Thank you so much for your kind help.

Eigenvalue problems are solved with SLEPc.
This has been illustrated in many posts on the forum (for instance: Eigenvalue solver problem) and in the documentation I’ve already referred you to.

Please spend some time reading through the demos and related posts before asking further questions.