[petsc-users] Natural norm

Jed Brown jed at jedbrown.org
Mon Sep 22 11:42:07 CDT 2014

Barry Smith <bsmith at mcs.anl.gov> writes:
>    All true. Switching the CG “norm” does not effect the algorithm (in
>    exact arithmetic) it only affects the norm that is printed and when
>    the algorithm stops. The same minimization principles hold
>    independent of the “norm” used.

Yup, and the natural norm avoids the need for an extra reduction.  If
you're using classic (non-pipelined and not single_reduction) CG in a
latency-sensitive environment, then you might benefit from using the
natural norm.
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