[petsc-users] chowiluviennacl

[Matthew Knepley]

On Wed, Jan 15, 2020 at 1:48 PM Xiangdong <epscodes at gmail.com> wrote:

> In the ViennaCL manual
> http://viennacl.sourceforge.net/doc/manual-algorithms.html
>
> It did expose two parameters:
>
> // configuration of preconditioner:
> viennacl::linalg::chow_patel_tag chow_patel_ilu_config;
> chow_patel_ilu_config.sweeps(3); // three nonlinear sweeps
> chow_patel_ilu_config.jacobi_iters(2); // two Jacobi iterations per
> triangular 'solve' Rx=r
>
> and mentioned that:
> The number of nonlinear sweeps and Jacobi iterations need to be set
> problem-specific for best performance.
>
> In the PETSc' implementation:
>
> viennacl::linalg::chow_patel_tag ilu_tag;
>     ViennaCLAIJMatrix *mat = (ViennaCLAIJMatrix*)gpustruct->mat;
>     ilu->CHOWILUVIENNACL = new
> viennacl::linalg::chow_patel_ilu_precond<viennacl::compressed_matrix<PetscScalar>
> >(*mat, ilu_tag);
>
> The default is used. Is it possible to expose these two parameters so that
> user can change it through option keys?
>

Yes. Do you mind making an issue for it? That way we can better keep track.

https://gitlab.com/petsc/petsc/issues

  Thanks,

    Matt


> Thank you.
>
> Xiangdong
>
> On Wed, Jan 15, 2020 at 12:40 PM Matthew Knepley <knepley at gmail.com>
> wrote:
>
>> On Wed, Jan 15, 2020 at 9:59 AM Xiangdong <epscodes at gmail.com> wrote:
>>
>>> Maybe I am not clear. I want to solve the block tridiagonal system  Tx=b
>>> a few times with same T but different b. On CPU, I can have it by applying
>>> the ILU0 and reuse the factorization. Since it is block tridiagonal, ILU0
>>> would give same results as LU.
>>>
>>> I am trying to do the same thing on GPU with chowiluviennacl, but found
>>> default factorization does not produce the exact factorization for
>>> tridiagonal system. Can we tight the drop off tolerance so that it can work
>>> as LU for tridiagonal system?
>>>
>>
>> There are no options in our implementation. You could look at the
>> ViennaCL manual to see if we missed something.
>>
>>   Thanks,
>>
>>     Matt
>>
>>
>>> Thank you.
>>>
>>> Xiangdong
>>>
>>> On Wed, Jan 15, 2020 at 9:41 AM Matthew Knepley <knepley at gmail.com>
>>> wrote:
>>>
>>>> On Wed, Jan 15, 2020 at 9:36 AM Xiangdong <epscodes at gmail.com> wrote:
>>>>
>>>>> Can chowiluviennacl do ilu0?
>>>>>
>>>>> I need to solve a tri-diagonal system directly. If I apply the PCILU,
>>>>> I will obtain the exact solution with preonly + pcilu. However, the
>>>>> preonly + chowiluviennacl will not provide the exact solution. Any option
>>>>> keys to set the CHOWILUVIENNACL filling level or dropping off tolerance
>>>>> like the standard ilu?
>>>>>
>>>>
>>>> No. However, such a scheme makes less sense here. This algorithm spawns
>>>> a individual threads for individual elements. Drop tolerance
>>>> is not less work, it is sparser, but that should not matter for a
>>>> tridiagonal system. Levels also is not applicable since you have only 1
>>>> level.
>>>>
>>>>   Thanks,
>>>>
>>>>     Matt
>>>>
>>>>
>>>>> Thank you.
>>>>>
>>>>> Best,
>>>>> Xiangdong
>>>>>
>>>>>
>>>>>
>>>>> On Tue, Jan 14, 2020 at 10:05 PM Matthew Knepley <knepley at gmail.com>
>>>>> wrote:
>>>>>
>>>>>> On Tue, Jan 14, 2020 at 9:56 PM Xiangdong <epscodes at gmail.com> wrote:
>>>>>>
>>>>>>> Dear Developers,
>>>>>>>
>>>>>>> I have a quick question about the chowiluviennacl. When I tried to
>>>>>>> use it, I found that it only works for np=1, not np>1. However, in the
>>>>>>> description of chowiluviennacl.cxx, it says "the ViennaCL Chow-Patel
>>>>>>> parallel ILU preconditioner".
>>>>>>>
>>>>>>
>>>>>> By parallel, this means shared memory parallelism on the GPU.
>>>>>>
>>>>>>
>>>>>>> I am wondering whether I am using it correctly. Does chowiluviennacl
>>>>>>> work for np>1?
>>>>>>>
>>>>>>
>>>>>> I do not believe so. I do not see why it could not be extended, but
>>>>>> that would mean writing some more code.
>>>>>>
>>>>>>   Thanks,
>>>>>>
>>>>>>     Matt
>>>>>>
>>>>>>
>>>>>>> In addition, are there option keys for the chowiluviennacl one can
>>>>>>> try?
>>>>>>> Thank you.
>>>>>>>
>>>>>>> Best,
>>>>>>> Xiangdong
>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> What most experimenters take for granted before they begin their
>>>>>> experiments is infinitely more interesting than any results to which their
>>>>>> experiments lead.
>>>>>> -- Norbert Wiener
>>>>>>
>>>>>> https://www.cse.buffalo.edu/~knepley/
>>>>>> <http://www.cse.buffalo.edu/~knepley/>
>>>>>>
>>>>>
>>>>
>>>> --
>>>> What most experimenters take for granted before they begin their
>>>> experiments is infinitely more interesting than any results to which their
>>>> experiments lead.
>>>> -- Norbert Wiener
>>>>
>>>> https://www.cse.buffalo.edu/~knepley/
>>>> <http://www.cse.buffalo.edu/~knepley/>
>>>>
>>>
>>
>> --
>> What most experimenters take for granted before they begin their
>> experiments is infinitely more interesting than any results to which their
>> experiments lead.
>> -- Norbert Wiener
>>
>> https://www.cse.buffalo.edu/~knepley/
>> <http://www.cse.buffalo.edu/~knepley/>
>>
>

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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