How to read data from class Matrix?

Question

Hi, I am new here. Could I ask how to read out the matrix in class Matrix? For example, in the following code, if I want to read the data in A after assembling, what should I do?

So thanks for the helps!

from dolfin import * 
import numpy
# Create mesh and define function space
nx = ny = 2
mesh = UnitSquare(nx, ny)
V = FunctionSpace(mesh, 'Lagrange', 1)
dt = 0.3      # time step
# Define variational problem
u = TrialFunction(V)
v = TestFunction(V)
a = u*v*dx + dt*inner(nabla_grad(u), nabla_grad(v))*dx
A = assemble(a)   # assemble

Comments

What do you mean by 'read the data'? Do you want to print the matrix to the screen?

Answer 1

You can get a NumPy array representation by running A.array().

Answer 2

If you want to avoid densification of the sparse operator matrix, you would have to use the uBLAS backend.

import scipy.sparse as sps
parameters.linear_algebra_backend = "uBLAS"
rows, cols, values = A.data()
Aa = sps.csr_matrix((values, cols, rows))