Assemble with dolfin VS dolfinx

dolfinx
2

This is because setting dof values to a RT array doesn’t really make sense.
You should be quite careful with this, as the degrees of freedom relate to vector basis functions.

Here is a way to illustrate the same, but with an actually well defined function (the constant vector (2,1,3), you could change this to (1,1,1) if you want to)

# # Using Dolfinx

try:
    import dolfinx as dlfx
    from mpi4py import MPI
    import ufl
    import numpy as np

    def f(x):
        values = np.zeros((3, x.shape[1]))
        values[0] = 2
        values[1] = 1
        values[2] = 3
        return values

    mesh_dlfx = dlfx.mesh.create_unit_cube(MPI.COMM_WORLD,
                                           10,
                                           10,
                                           10,
                                           dlfx.mesh.CellType.tetrahedron)
    V_dlfx = dlfx.fem.functionspace(mesh_dlfx, ("RT", 1))
    f_dlfx = dlfx.fem.Function(V_dlfx)
    f_dlfx.interpolate(f)
    vol_dlfx = dlfx.fem.assemble_scalar(dlfx.fem.form(
        dlfx.fem.Constant(mesh_dlfx, 1.0) * ufl.dx))
    res_dlfx = dlfx.fem.assemble_scalar(
        dlfx.fem.form(ufl.dot(f_dlfx, f_dlfx)**(1/2) * ufl.dx))
    print("dolfinx")
    print(f"{vol_dlfx=}")
    print(f"{res_dlfx=}")


except ImportError:
    # Using Dolfin
    import dolfin as dlf
    mesh_dlf = dlf.BoxMesh(dlf.Point(0.0, 0.0, 0.0),
                           dlf.Point(1.0, 1.0, 1.0),
                           10, 10, 10)
    V_dlf = dlf.FunctionSpace(mesh_dlf, "RT", 1)
    f_dlf = dlf.Function(V_dlf)
    f_dlf.interpolate(dlf.Expression(("2", "1", "3"), degree=1))
    vol_dlf = dlf.assemble(dlf.Constant(
        1) * dlf.Measure('dx', domain=mesh_dlf))
    res_dlf = dlf.assemble(dlf.dot(f_dlf, f_dlf)**(1/2) * dlf.dx)
    print("legacy dolfin")
    print(f"{vol_dlf=}")
    print(f"{res_dlf=}")

yields

dolfinx
vol_dlfx=0.9999999999999232
res_dlfx=3.7416573867708562

and

legacy dolfin
vol_dlf=0.9999999999999232
res_dlf=3.74165738677434
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