[petsc-users] PCGASMSetLocalSubdomains

[Hui Zhang]

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.  I'm solving the Helmholtz equation.  Maybe 
I can prepare a simpler example to show this difference.

> 
> 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> 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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