Mass Lumping in dolfinx

[maxre]

Thanks for noticing the typo! What a rookie mistake on my side…
Also, I was able to solve the problem myself in the meantime based on the following topic:

Set integration rule to closed/vertex

I want to set the integration rule to closed for all terms of my problem and not only the mass matrix. I have a MWE on the unit interval with P1 elements and a term f = x from dolfinx import mesh, fem import ufl from mpi4py import MPI nx = 2 domain = mesh.create_unit_interval(MPI.COMM_WORLD, nx) V = fem.FunctionSpace(domain, ("CG", 1)) x = ufl.SpatialCoordinate( domain ) function = x[0] v = ufl.TestFunction(V) b = function*v*ufl.dx linear_form = fem.form(b) b = fem.petsc.create_vector(lin…

The correct way would be:
dxL = ufl.Measure("dx", metadata = {"quadrature_rule": "vertex"})
I am not fully sure about further meta-settings. But for now it works in my application.

The whole MWE that compares the methods.

import numpy as np
from mpi4py import MPI
from dolfinx import mesh
from dolfinx.fem.petsc import assemble_matrix
from dolfinx.fem import VectorFunctionSpace, Function 

domain = mesh.create_unit_square(MPI.COMM_WORLD, 8, 8, mesh.CellType.triangle)
V = VectorFunctionSpace(domain, ("Lagrange", 1), dim =2)
from dolfinx import fem
import numpy
import ufl
u = ufl.TrialFunction(V)
u0 = Function(V)
v = ufl.TestFunction(V)
# Mass Lumping
dxL = ufl.Measure("dx", metadata = {"quadrature_rule": "vertex"})
Eqa = ufl.inner(u, v)*ufl.dx
Eqb = ufl.inner(u,v)*dxL

Xa= assemble_matrix(fem.form(Eqa))
Xb= assemble_matrix(fem.form(Eqb))
Xa.assemble()
Xb.assemble()
Xa.convert("dense")
Ca = Xa.getDenseArray()
Xb.convert("dense")
Cb = Xb.getDenseArray()
print("w/o mass lumping \n",Ca)
print("w/ mass lumping \n",Cb)
print("difference: ", np.max(np.abs(Ca-Cb)))
only_diagonal = True
for i in range(len(Cb)):
    for j in range(len(Cb[0])):
        if i!=j:
            if Cb[i][j] != 0.0:                
                only_diagonal=False

print("only values on the diagonal: ",only_diagonal)