[petsc-users] chowiluviennacl

[Xiangdong]

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?

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/>
>
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