How to get the trace of a ufl mass matrix form

Question

Hi,

The question is, given a ufl form with a mass matrix of a problem:

m = inner(u, v)*dx

how can i calculate the trace (first invariant) of it?. I already try with:

Aij = v[i]*v[j]
A = as_tensor(Aij, (i,j))
t = tr(A)

but t doesn't contain explicitly the value of the trace of A, and i need to see it.

Thanks in advice!

Answer 1

Hi, if PETSc is your linear algebra backend consider:

m = assemble(inner(u, v)*dx)
diag = as_backend_type(m).mat().getDiagonal().array
trace = diag.sum()
print trace

regards!