[petsc-users] chowiluviennacl

[Matthew Knepley]

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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