[petsc-dev] PETSC application

[Matthew Knepley]

On Sun, Mar 7, 2010 at 12:20 PM, David sheehan <david.sheehanjr at gmail.com>wrote:

> >I mean Ax =b doesn't have A in explicit form, but in expression
> A=B+C1+C2+...+Cn,
> >where B is main part of A in an explicit form, C1, C2,... and Cn are small
> portions
> >comparing with B and they don't have an explicit form. Thus I want  to
>  make a
> >preconditioner from B, then apply the preconditioner to Ax=b. Please tell
> me how I
> >can do by PETSC sentences for PETSC solver, thanks.
>
> >   call KSPSetOperators(ksp,A,B,......)
>
> However, A doesn't have an explicit matrix form, how to call
> call KSPSetOperators(ksp,A,B,......)
>

Use MATSHELL for A.

   Matt


> ?  thanks.
>
> Based on what I thought, once I got preconditioner of B, I am wondering if
> I can
> define a special matrix-vector multiplication for A=B+C1+C2+...+Cn from a
> PETSC
> sentence, such that it can do following
> 1) x1=B*x
> 2) x2=x1+ C1*x, where C1*x is a sequence of matrix-vector multiplications
> 3) x3= x2+C2*x,......
> .....
> 4) xn+1=xn+Cn*x,where Cn*x is a squence of matrix-vector multiplications
>
> Then select a KSP iterative method such as GMRES to use the above
> matrix-vector
> multiplication and preconditioner that I made from B.
>
> Could you please tell me if it is possible? if so (I hope), how can I do it
> ? thanks.
>
> David
>
> On Sun, Mar 7, 2010 at 11:12 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
>>
>>  On Mar 7, 2010, at 10:57 AM, David sheehan wrote:
>>
>>  >First, configure with Hypre .
>> You mean, configure for the installation of PETSC with hypre? thanks.
>>
>>    yes, add --download-hypre
>>
>>
>> >Then -pc_type hypre -pc_hypre_type boomeramg
>> You mean, without adding any information into code include, just compile
>> and link
>> the code, to get an excuteable file, e.g. "a.out", then
>> a.out -pc_type hypre -pc_hypre_type boomeramg
>> is it right? thanks.
>>
>>
>>    Yes,
>>
>>
>> >I cannot understand exactly what you mean. However, if you want to create
>> a PC
>> > based upon a >matrix which is not the system matrix A, you can specify
>> it in
>> > KSPSetOperators().
>>
>> I mean Ax =b doesn't have A in explicit form, but in expression
>> A=B+C1+C2+...+Cn,
>> where B is main part of A in an explicity form, C1, C2,... and Cn are
>> small portions
>> comparing with B and they don't have an explicit form. Thus I want  to
>>  make a
>> preconditioner from B, then apply the preconditioner to Ax=b. Please tell
>> me how I
>> can do by PETSC sentences for PETSC solver, thanks.
>>
>>
>>    call KSPSetOperators(ksp,A,B,......)
>>
>>    Barry
>>
>>
>>
>>
>> David
>>
>>
>> On Sun, Mar 7, 2010 at 12:32 AM, Matthew Knepley <knepley at gmail.com>wrote:
>>
>>> On Sat, Mar 6, 2010 at 11:49 PM, David sheehan <
>>> david.sheehanjr at gmail.com> wrote:
>>>
>>>> Hi,
>>>> I need your helps about PETSC as follows:
>>>> 1) how can I call boomerAMG of HYPRE through PETSC as a solver and a
>>>> preconditioner?
>>>>
>>>
>>> First, configure with Hypre . Then -pc_type hypre -pc_hypre_type
>>> boomeramg
>>>
>>>
>>>> 2) how can I make a precondioner  from B matrix,  but apply the
>>>> preconditioner to Ax=b in PETSC?
>>>> Thanks in advance.
>>>>
>>>
>>> I cannot understand exactly what you mean. However, if you want to create
>>> a PC based upon a matrix
>>> which is not the system matrix A, you can specify it in
>>> KSPSetOperators().
>>>
>>>   Matt
>>>
>>>
>>>> David
>>>>
>>> --
>>> 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
>>>
>>
>>
>>
>


-- 
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
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