Real elements with non-linear problems

[RemDelaporteMathurin]

I have a nonlinear problem and would like to be able to use real elements.

So I tried doing:

from mpi4py import MPI
import dolfinx
import numpy as np
from scifem import create_real_functionspace
import ufl

M = 20
mesh = dolfinx.mesh.create_unit_interval(MPI.COMM_WORLD, M, dtype=np.float64)
V = dolfinx.fem.functionspace(mesh, ("Lagrange", 1))
R = create_real_functionspace(mesh)

W = ufl.MixedFunctionSpace(V, R)


u = fem.Function(W)

But this doesn't seem to work:

Traceback (most recent call last):
  File "/home/remidm/FESTIM/example_real_element.py", line 20, in <module>
    u = dolfinx.fem.Function(W)
  File "/home/remidm/anaconda3/envs/festim2-dev/lib/python3.13/site-packages/dolfinx/fem/function.py", line 319, in __init__
    V.element.dtype, np.dtype(dtype).type(0).real.dtype
    ^^^^^^^^^
AttributeError: 'MixedFunctionSpace' object has no attribute 'element'

Is this supported by scifem or is it limited to TrialFunction for linear problems?

[RemDelaporteMathurin]

Oh I just saw #93 so it may be a duplicate

[jorgensd]

Instead of creating a function of the MixedFunctionSpace, create a Function in each sub-space (i.e. V and R) and use them throughout the code. In turn, you can pass these as a list to the new DOLFINx NonLinearProblem

[RemDelaporteMathurin]

understood thank you! I'll make a MWE post it here for others and then close this

[jorgensd]

IF you make an MWE, we could make it part of the SCIFEM documentation to help others:)

[RemDelaporteMathurin]

Will do!

[RemDelaporteMathurin]

the new DOLFINx NonLinearProblem

Does that mean I need dolfinx 0.10?

[RemDelaporteMathurin]

Started there

[RemDelaporteMathurin]

I believe I now have a working version of this, I have some instabilities in some situations so it probably needs some work.

@jorgensd shall I start a PR to add a demo?

[RemDelaporteMathurin]

Shall we close this and #191 now that dolfinx 0.11 is out?