[petsc-users] PCGASMSetLocalSubdomains

Hui Zhang mike.hui.zhang at hotmail.com
Sun May 20 10:00:10 CDT 2012 

On May 20, 2012, at 4:36 PM, Dmitry Karpeev wrote:

> 
> 
> On Sun, May 20, 2012 at 5:06 AM, Hui Zhang <mike.hui.zhang at hotmail.com> wrote:
> I have the following MatView output: 
> 
> row 0: (0, -0.0351719 - 0.638814 i) (1, -0.517586 - 0.617823 i) (4, -0.517586 - 0.617823 i) (1, -1.03517)  (5, -0.508793) 
> 
> Note that there are two values for the column 1, is this normal?
> 
> The above matrix is obtained from PCASMGetSubKSP(pc,subksp) and KSPGetOperators(subksp[0], ...).
> 
> This is odd. Can you explain a bit more what leads up to this, so we can try and reproduce the problem?

Yes, I will try to make a simple example program.  




> Thanks.
> Dmitry.
> 
> Thanks!
> 
> 
> 
> On May 11, 2012, at 7:17 PM, Dmitry Karpeev wrote:
> 
>> You can call PCSetUp(pc) on either ASM or GASM, and that will destroy and recreate the matrices (including calling 
>> your modification subroutine), but not the subdomains or the subdomain solvers. 
>> If you just want to modify the submatrices, you can call PC(G)ASMGetSubmatrices() and modify the matrices it returns
>> (in the same order as the subdomains were set). That's a bit of a hack, since you will essentially be modifying the PC's internal data structures.  As long as you are careful, you should be okay, since you already effectively have the same type of access to the submatrices through the Modify callback.
>> 
>> Dmitry.
>> 
>> On Fri, May 11, 2012 at 11:52 AM, Hui Zhang <mike.hui.zhang at hotmail.com> wrote:
>> 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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