[petsc-users] chowiluviennacl

[Xiangdong]

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?

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/>
>
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