Interpolate expression with complex litteral

dolfinx
1

Hello,

I am not sure why, but the following MWE does not work

import dolfinx, dolfinx.mesh
from dolfinx import fem
from mpi4py import MPI

mesh = dolfinx.mesh.create_unit_cube(MPI.COMM_WORLD, 5, 5, 5)
V = fem.FunctionSpace(mesh, ("CG", 1))

u = fem.Function(V)
u.vector.set(0.)

f = fem.Function(V)
expr = 1j * u

f.interpolate(fem.Expression(expr, V.element.interpolation_points))

which yields the following error

TypeError: can't convert complex to float

This is actually not a very big deal, as a trivial workaround would be the following

import dolfinx, dolfinx.mesh
from dolfinx import fem
from mpi4py import MPI

mesh = dolfinx.mesh.create_unit_cube(MPI.COMM_WORLD, 5, 5, 5)
V = fem.FunctionSpace(mesh, ("CG", 1))

u = fem.Function(V)
u.vector.set(0.)

im = fem.Function(V)
im.vector.set(1j)

f = fem.Function(V)
expr = im * u

f.interpolate(fem.Expression(expr, V.element.interpolation_points))

but still, I find it quite odd that the use of a complex litteral in an expression results in an error.
Is this intended?
Thanks!

2

Did you try specifying the dtype in the Expression constructor’s argument list?

3

Just tried to do so

f.interpolate(fem.Expression(expr, V.element.interpolation_points, dtype=np.complex128))

but the error persists. Anyway, from the Expression tooltip, dtype defaults to PETSc.ScalarType which is already set to np.complex128.

4

Could you try with dolfinx.fem.Constant(mesh, PETSc.ScalarType(1j))*u?

2 Likes
5

Yes it works using your code or even expr = dolfinx.fem.Constant(mesh, 1j)*u.