[petsc-users] PCGASMSetLocalSubdomains

[Dmitry Karpeev]

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?
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>
>>>>>> 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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