[petsc-users] PCGASMSetLocalSubdomains

Hui Zhang mike.hui.zhang at hotmail.com
Wed Feb 15 04:19:54 CST 2012

Hi Dmitry,

thanks a lot! Currently, I'm not using ISColoring. Just comes another question
on PCGASMSetModifySubMatrices(). The user provided function has the prototype

    func (PC pc,PetscInt nsub,IS *row,IS *col,Mat *submat,void *ctx);

I think the coloumns from the parameter 'col' are always the same as the rows 
from the parameter 'row'. Because PCGASMSetLocalSubdomains() only accepts 
index sets but not rows and columns. Has I misunderstood something?


On Feb 11, 2012, at 3:36 PM, Dmitry Karpeev wrote:

> Yes, that's right.
> There is no good way to help the user assemble the subdomains at the moment beyond the 2D stuff.
> It is expected that they are generated from mesh subdomains.
> Each IS does carry the subdomains subcomm.
> There is ISColoringToList() that is supposed to convert a "coloring" of indices to an array of ISs,
> each having the indices with the same color and the subcomm that supports that color. It is
> largely untested, though.  You could try using it and give us feedback on any problems you encounter.
> Dmitry.
> On Sat, Feb 11, 2012 at 6:06 AM, Hui Zhang <mike.hui.zhang at hotmail.com> wrote:
> About PCGASMSetLocalSubdomains(), in the case of one subdomain supported by
> multiple processors, shall I always create the arguments 'is[s]' and 'is_local[s]'
> in a subcommunicator consisting of processors supporting the subdomain 's'?
> The source code of PCGASMCreateSubdomains2D() seemingly does so.
> Thanks,
> Hui

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