[petsc-users] Questions regarding nested field split

[Matthew Knepley]

On Fri, Feb 25, 2022 at 2:40 PM Sundar Namala <solomon.sundar.n at gmail.com>
wrote:

> Hi, I am currently using fieldsplit and I am creating the fields using
> ISCreateGeneral.programming is being carried out in FORTRAN. I have a
> couple of questions regarding fieldsplit in parallel.
>
> Do we need to create the index list of all the fields separately for each
> processor?
>
> For example, say I have 3 fields and the indices for field_0 is 0-99,
> field_1 is 100-299 and field_2 is 300-349. In case of 2 processors do I
> have to specify the indices for the first processor as field_0 is 0-99,
> field_1 is 100-174 and field_2 is null. On the second processor field_0 is
> null, field_1 is 175-299 and field_2 is 300-349.
>

Yes, each process specifies its indices independently (and for each field).


> my second question is if the indices need to be listed separately how do
> you assign the null index list using ISCreateGeneral.
>

You can use an IS with size 0.

  Thanks,

     Matt


> Thanks,
> Sundar.
>


-- 
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

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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