Where to find 'project'-function in dolfinx?

dolfinx
4

See for instance: Error control: Computing convergence rates — FEniCSx tutorial
or:
Test problem 1: Channel flow (Poiseuille flow) — FEniCSx tutorial
ref

import numpy as np
def u_exact(x):
    values = np.zeros((2, x.shape[1]), dtype=PETSc.ScalarType)
    values[0] = 4*x[1]*(1.0 - x[1])
    return values
u_ex = Function(V)
u_ex.interpolate(u_exact)

L2_error = form(dot(u_ - u_ex, u_ - u_ex)*dx)
# do stuff
# ....
for i in range(num_steps):
    # Solve problem
    #....

    # Compute error at current time-step
    error_L2 = np.sqrt(mesh.comm.allreduce(assemble_scalar(L2_error), op=MPI.SUM))

I would also like to note that you do not need the project functionality for computing the error “pointwise”, i.e.

could be handled with dolfinx.fem.Expression and interpolate, see for instance: Problem with grad and interpolate - #2 by dokken

I am also not sure why you do not just call

error_normalized = (u_ref - u_approx) / u_ref
error_total = sqrt(assemble(inner(error_normalized, error_normalized) * dx))

in DOLFIN, or the equivalent version of it in DOLFINx.

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