Convert a numpy array to a vector in dolfin with discontinuous space

1

Dear Fenics community,

I’m facing an issue when trying to convert a numpy array into a dolfin vector, when the function space (a subspace in my case) is discontinuous. The example is as follows:

from dolfin import *
import numpy as np
l = 4.0
DOF = 50

mesh = IntervalMesh(DOF, 0, l)

degree = 1

P1 = FiniteElement("Lagrange", interval, degree)

P0 = FiniteElement("Discontinuous Lagrange", interval, degree-1)

element = MixedElement([P1, P0])

U = FunctionSpace(mesh, element)

# Numpy array
w_array = np.random.rand(DOF+1)

# Function on DG subspace
w_f = Function(U.sub(1).collapse())

# Numpy to dof assign
w_f.vector()[:] = w_array[:]

However, I get the following Runtime error:

*** -------------------------------------------------------------------------
*** DOLFIN encountered an error. If you are not able to resolve this issue
*** using the information listed below, you can ask for help at

*** fenics-support@googlegroups.com

*** Remember to include the error message listed below and, if possible,
*** include a minimal running example to reproduce the error.

*** -------------------------------------------------------------------------
*** Error: Unable to set local values of PETSc vector.
*** Reason: Size of values array is not equal to local vector size.
*** Where: This error was encountered inside PETScVector.cpp.
*** Process: 0

*** DOLFIN version: 2019.1.0
*** Git changeset: unknown

Am I missing something?. Any help is appreciated.

Thanks!.

2

The following seems to work:

# Numpy array
#w_array = np.random.rand(DOF+1)
w_array = np.random.rand(DOF)

Keep in mind that the DG0 space has one fewer degrees of freedom than the CG1 space.

3

Dear kamensky,

The code work as expected. The question is mark as solved.

Thank you.