On Thu, Jun 23, 2011 at 11:03 AM, Jed Brown <jed at 59a2.org> wrote: > On Thu, Jun 23, 2011 at 16:59, John Fettig <john.fettig at gmail.com> wrote: >> >> I understand everything you say here except what "compressing" means. >> It is compressed by virtue of being in CSR format, but then you do >> some additional mapping with the column indices that further >> compresses it? What purpose does changing the column indices serve? > > It operates on the dense vector consisting of only those entries on other > processors that interact with the current one. If this thing operated on the > full global vector, there would either need to be a matrix format that could > operator on "sparse vectors" (i.e. an additional layer of indirection) or > the whole dense global vector would need to be gathered to every process > which would be horribly non-scalable.
Thanks for the explanation, it makes sense. John
