[petsc-users] Speed of MatGetRowSum

[Derek Gaston]

I was wondering about the comment on MatGetRowSum that says:

"This code is slow since it is not currently specialized for different
formats"

How slow are we talking about here?  Is it actually going to loop over i,j
from 0 to N on a sparse matrix?

I need to get a vector that represents the "lumped" mass matrix: but I
would like to get it fairly quickly.  I would just compute the lumped
matrix directly and then use MatGetDiag - but I actually want both
(unlumped/consistent and lumped) and MatGetRowSum seemed like the best
direction.  Willing to take advice though!

Derek
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