On Feb 21, 2014, at 11:02 AM, Fischer, Greg A. <[email protected]>
wrote:
> Hello,
>
> I’m interested in using PETSc to manage distributed arrays. Based on my
> reading about the DMDA objects, I see that ghost points can be communicated
> in box-type stencils or star-type stencils.
>
> For my application, assume that I have a 2D DMDA object with star-type
> stencils. For a typical local calculation, I only need to access ghost values
> from two of the four directions at a time. For example, I’d like access to
> ghost values in the South and East directions, but not in the North or West
> directions. Communicating North and West data would seem to be wasting
> bandwidth. Is there any way to accomplish this?
Greg,
There is not anything built in. Here is what I suggest:
1) write your application code not worrying about the fact that the
DMGlobalToLocalBegin/End() is moving values you don’t need.
2) when your code is running correctly for your problem and giving useful
results if the communication times are impacting how long it takes to run you
can provide a custom communication pattern. It would involve little additional
coding essentially taking DMSetUp_DA_2D() which creates the list of ghost
points and removing the unneeded ghost points. But it would be premature to
do this optimization until you have a full working application code.
Barry
>
> Thanks,
> Greg
