[petsc-users] question about DA

[Likun Tan]

Okay, i c, thanks.

So if i want to sum over the z direction, it is better not to partition in
z direction, i just tried and it works.

Another question is, if the size is small in x and y directions, and large
in z direction, i want more of processors, but the number is restricted to
the size in x and y direction, since partition is not allowed in z
direction, any way to improve efficiency?



On Sat, August 27, 2011 5:54 pm, Jed Brown wrote:
> On Sat, Aug 27, 2011 at 16:49, Likun Tan <likunt at andrew.cmu.edu> wrote:
>
>
>> I am sorry i still don't get what my problem is, i though when setting
>> values to 2D, x, y, m and n will be reset, so the previous usage of the
>> corner indices and width won't influence the later use.
>>
>
> The whole array is not duplicated onto every process, just the owned part
>  and perhaps ghosts. You have to make sure that the decompositions are
> compatible and that you only index into the part of the array that your
> process has access to. This is really unlikely to happen "by accident",
> so you have to decide how you want the total volume decomposed and which
> parts you want local. Part of this (typically, if you are going to
> integrate) is to not decompose at all in the z direction. Once you ensure
> that everything is compatible, you can have one accessor that gives you
> the array bounds for the 3D part and use the 2D part in a compatible way.
>