[petsc-users] randomness from MATSOLVERPACKAGE

Jed Brown jedbrown at mcs.anl.gov
Wed May 30 09:40:25 CDT 2012

On Wed, May 30, 2012 at 9:37 AM, Hui Zhang <mike.hui.zhang at hotmail.com>wrote:

> How is the matrix assembled?
> In a deterministic way.

Do you use ADD_VALUES with off-process entries? If so, the message order
may be different. You can also add -vecscatter_reproduce to make VecScatter
with ADD_VALUES process the messages in a static order instead of in the
order they arrive (somewhat slower).

> How different?
> Not very much. The last residual can vary in its trailing digits, e.g.
> from 6.5819e-7 to 6.5820e-7

This looks fine.
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