[petsc-users] Compute the sum of the absolute values of the off-block diagonal entries of each row

[Cyrill Vonplanta]

Dear Petsc Users,

I am trying to implement a variant of the $l^1$-Gauss-Seidel smoother from https://doi.org/10.1137/100798806 (eq. 6.1 and below). One of the main issues is that I need to compute the sum  $\sum_j |a_{i_j}|$ of the matrix entries that are not part of the local diagonal block. I was looking for something like MatGetRowSumAbs but it looks like it hasn't been made yet.

I guess i have to come up with something myself, but would you know of some workaround for this without going too deep into PETCs?

Best Cyrill