[petsc-users] PCGASMSetLocalSubdomains

[Dmitry Karpeev]

On Mon, Feb 20, 2012 at 12:59 AM, Hui Zhang <mike.hui.zhang at hotmail.com>wrote:

>
> On Feb 20, 2012, at 12:41 AM, Dmitry Karpeev wrote:
>
>
>
> On Sun, Feb 19, 2012 at 3:08 PM, Hui Zhang <mike.hui.zhang at hotmail.com>wrote:
>
>> I have a new problem: the results from ASM and GASM are different and it
>> seems
>> GASM has something wrong with SetModifySubMatrices. Numerical tests are
>> with
>> each subdomain supported only by one subdomain. There are no problems when
>> I did not modify submatrices.  But when I modify submatrices, there are
>> problems
>> with GASM but no problems with ASM.
>>
>> For example, I use two subdomains. In the first case each subdomain is
>> supported by
>> one processor and there seems no problem with GASM. But when I use run my
>> program
>> with only one proc. so that it supports both of the two subdomains, the
>> iteration
>> number is different from the first case and is much larger.  On the other
>> hand
>> ASM has no such problem.
>>
>
> Are the solutions the same?
> What problem are you solving?
>
>
> Yes, the solutions are the same. That's why ASM gives the same results
> with one or
> two processors. But GASM did not.
>
Sorry, I wasn't clear: ASM and GASM produced different solutions in the
case of two domains per processor?

> I'm solving the Helmholtz equation.  Maybe
> I can prepare a simpler example to show this difference.
>
That would be helpful.
Thanks.

Dmitry.

>
>
> Dmitry.
>
>>
>>
>> On Feb 15, 2012, at 6:46 PM, Dmitry Karpeev wrote:
>>
>> You should be able to.
>> This behavior is the same as in PCASM,
>> except in GASM the matrices live on subcommunicators.
>> I am in transit right now, but I can take a closer look in Friday.
>>
>> Dmitry
>>
>>
>>
>> On Feb 15, 2012, at 8:07, Hui Zhang <mike.hui.zhang at hotmail.com> wrote:
>>
>> On Feb 15, 2012, at 11:19 AM, Hui Zhang wrote:
>>
>> 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?
>>
>>
>> As I tested, the row and col are always the same.
>>
>> I have a new question. Am I allowed to SetLocalToGlobalMapping() for the
>> submat's
>> in the above func()?
>>
>> thanks,
>> Hui
>>
>>
>> thanks,
>> Hui
>>
>>
>> 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>
>> 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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