On Tue, Jan 3, 2012 at 16:44, Jack Poulson <jack.poulson at gmail.com> wrote:
> It is possible, though unlikely that the BLAS dot could be faster than the > BLAS nrm2, though I am skeptical. The reason is that the result of dnrm2 on > a vector u is more stable than the square root of the inner product of u > with itself via ddot, as it scales the temporary products of the norm to > make the computation more accurate: > http://www.netlib.org/blas/dnrm2.f > Ah, thanks for pointing this out. > > > Thus, if you don't care about accuracy, then it is _possible_ that ddot > would be faster, but i doubt it, and it is likely a bad idea to give up on > some stability. > Agreed. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20120103/0caca10c/attachment.html>
