[petsc-users] parallel interpolation?

[Matthew Knepley]

On Tue, Feb 17, 2015 at 7:46 AM, Gideon Simpson <gideon.simpson at gmail.com>
wrote:

> Suppose I have data in Vec x and Vec y, and I want to interpolate this
> onto Vec xx, storing the values in Vec yy.  All vectors have the same
> layout.  The problem is that, for example, some of the values in xx on
> processor 0 may need the values of x and y on processor 1, and so on.
> Aside from just using sequential vectors, so that everything is local, is
> there a reasonable way to make this computation?
>

At the most basic linear algebra level, you would construct a VecScatter
which mapped the pieces you need from other processes into a local vector
along with the local portion, and you would use that to calculate values,
which you then put back into your owned portion of a global vector. Thus
local vectors have halos and global vectors do not.

If you halo regions (values you need from other processes) have a common
topology, then we have simpler
support that will make the VecScatter for you. For example, if your values
lie on a Cartesian grid and you
just need neighbors within distance k, you can use a DMDA to express this
and automatically make the
VecScatter. Likewise, if you values lie on an unstructured mesh and you
need a distance k adjacency,
DMPlex can create the scatter for you.

If you are creating the VecScatter yourself, it might be easier to use the
new PetscSF instead since it only needs one-sided information, and performs
the same job. This is what DMPlex uses to do the communication.

  Thanks,

     Matt


> -gideon
>
>


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