Interpolation of non-symmetric tensor into a symmetric space

[mscroggs]

Describe new/missing feature

Currently if you interpolate a non-symmetric tensor into a symmetric space, it will ignore the part above the diagonal.

For example (once #3164 is fixed), the following code will print [1. 2. 4. 2. 3. 5. 4. 5. 6.] even though the input has 0s above the diagonal.

import basix.ufl
import numpy as np
from dolfinx.mesh import create_unit_square
from dolfinx.fem import functionspace, Function
from mpi4py import MPI

mesh = create_unit_square(MPI.COMM_WORLD, 10, 10)

def tensor(x):
    mat = np.array([[1], [0], [0], [2], [3], [0], [4], [5], [6]])
    return np.broadcast_to(mat, (9, x.shape[1]))

element = basix.ufl.element("DG", mesh.basix_cell(), 0, shape=(3, 3), symmetry=True)
space = functionspace(mesh, element)
f = Function(space)
f.interpolate(lambda x: tensor(x))
print(f.eval([[0, 0, 0]], [0]))

I'm unsure what is the best thing to do in case like this

Suggested user interface

No response