Dominic,
DMLocalToLocal is the intended usage. There is code inside the VecScatter
to detect unneeded copies, which would result in only touching the ghost cells,
but for some reason that is not currently turned on, I'll take a look at
fixing it in master.
Barry
> On Mar 31, 2015, at 10:12 AM, Dominic Meiser <[email protected]> wrote:
>
> Hi,
>
> I have a DMDA for a structured grid in a 3D FDTD calculation. What is the
> most efficient way to update the ghost regions after each time step?
> Currently I update a global vector and then I scatter to a local vector using
> DMGlobalToLocalBegin/End for the next time step. I also tried DMLocalToLocal
> with the same source and target vector and that appears to be slightly
> faster, perhaps due to better cache usage in the copy of the owned region.
> Ideally I would like to update just the ghost cells from the owned regions.
> Is there a good way to do that? Something similar to VecGhostUpdateBegin/End?
>
> Thanks,
> Dominic
>
> --
> Dominic Meiser
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>
