[petsc-users] PCGASMSetLocalSubdomains

[Hui Zhang]

I just have a question about reuse of PCASM or PCGASM.
Suppose I have seted up the PCASM and related KSP and I solved one time.
Next for the same linear system (matrix and RHS), I just want PCASM modify the submatrices (PCSetModifySubmatrices) in a different way, using the same routine for modifying but with
different user context for the modifying routine.  

What can I do for this task?  Currently, I destroy the KSP and re-construct it. I guess
even for PCASM I can re-use it because the partition of subdomains remain the same.

Thanks!


On May 10, 2012, at 6:37 PM, Dmitry Karpeev wrote:

> Hui,
> There've been several changes to PCGASM ahead of the new release.
> Let me go back and see if it affected the convergence problem.
> Dmitry.
> 
> On Thu, May 10, 2012 at 4:16 AM, Hui Zhang <mike.hui.zhang at hotmail.com> wrote:
> Hi Dmitry,
> 
> is there any news about PCGASM? 
> 
> thanks,
> Hui
> 
> On Feb 20, 2012, at 6:38 PM, Dmitry Karpeev wrote:
> 
>> Okay, thanks.
>> I'll take a look.
>> 
>> Dmitry.
>> 
>> On Mon, Feb 20, 2012 at 11:30 AM, Hui Zhang <mike.hui.zhang at hotmail.com> wrote:
>> For reference, my results are attached.
>> 
>> asm1.txt for asm with 1 process,
>> asm2.txt for asm with 2 processes,
>> gasm1.txt for gasm with 1 process, (with the iteration numbers different from others)
>> gasm2.txt for gasm with 2 processes
>> 
>> 
>> 
>> 
>> 
>> 
>> thank you,
>> Hui
>> 
>> On Feb 20, 2012, at 3:06 PM, Dmitry Karpeev wrote:
>> 
>>> 
>>> 
>>> 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> 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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