[petsc-users] matrix-matrix addition

[Jed Brown]

On Mon, Sep 27, 2010 at 19:01, Barry Smith <bsmith at mcs.anl.gov> wrote:
> If you do not merge the column indices from A and B but simply count them all you will get over allocation, at worst a factor of two, though usually it would just be a little.

You count the number of *unique* entries.  You have two indices that
run through the arrays aj and bj, counting duplicates only once.  This
is easy to do since they are both sorted.

Jed