Convert the solution in Function class and assembled operator to numpy array or scipy.csr_matrix vice and versa

[JunmingDuan]

Dear community,

I use firedrake to solve a problem: I can build the operator A and RHS b, and solve A*x=b to get x, which is Function.
Now I need to get the matrix and vector of A and x in scipy.csr_matrix and numpy array form, and also backward.
Could you help me on this?

Thank you in advance!
Junming

[connorjward]

Matrix

I have been hacking around and found the following solution to get a scipy csr_matrix from a Firedrake Matrix:

petsc_mat = firedrake_matrix.M.handle
ai, aj, av = petsc_mat.getValuesCSR()
scipy_matrix = scipy.sparse.csr_matrix((av, aj, ai))

Note that this should probably not be attempted in parallel.

For the inverse operation see this post.

Vector

Firedrake Functions are natively stored as numpy arrays so this is a simple operation. You just want function.dat.data