[petsc-dev] DMGetLocalToGlobalMapping(), can it be collective

Matthew Knepley knepley at gmail.com
Mon Nov 22 20:32:32 CST 2010

I am pro collective since I can't envision depending on the lack on


On Mon, Nov 22, 2010 at 7:06 PM, Jed Brown <jed at 59a2.org> wrote:

> I would like to make DMDAGetISLocalToGlobalMapping() DM-level functionality
> since it is an essential ingredient in the MatGetLocalSubMatrix-based
> assembly, but it's not an essential part of how every conceivable DM
> functions.  I would rather allocate that memory lazily so that not every
> user is required to pay for it (e.g. when they don't even have a matrix),
> but creating an ISLocalToGlobalMapping is a collective operation
> (somewhat strangely, because only the rarely used inversion of the map is a
> collective operation).  This means that either DMGetLocalToGlobalMapping
> becomes a collective operation, or everyone needs to pay for it to exist?
>  Thoughts?
> Jed

What most experimenters take for granted before they begin their experiments
is infinitely more interesting than any results to which their experiments
-- Norbert Wiener
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