[petsc-users] KSPBuildResidual

[jarunan at ascomp.ch]

Thanks for the suggestion.

Can I change residual norm from Norm 2 to infinity norm?


Regards,
Jarunan



Quoting Barry Smith <bsmith at mcs.anl.gov>:

>
>    If you want to use the true residual norm then use GMRES with right
> preconditioning. KSPSetPreconditionerSide()
>
>     Barry
>
> On Dec 23, 2009, at 5:01 AM, jarunan at ascomp.ch wrote:
>
>>
>> Dear Petsc-Team
>>
>> I am using KSPBuildResidual() to calculate true residual and use it  
>>  as convergence criteria. It means the program will call   
>> KSPBuildResidual every iteration. I choose GMRES as a solver but I   
>> read in manual, it is written that this command is expensive for   
>> GMRES and some other solvers.
>>
>> Is it also expensive for BICGSTAB?
>> Is there other possibility to calculate true residual without   
>> calling KSPBuildResidual() or KSPBuildSolution() ?
>>
>> Best regards,
>> Jarunan
>>
>>
>> Quoting Rob Ellis <Robert.G.Ellis at Shaw.ca>:
>>
>>> Hi Dave,
>>>
>>> Thanks! That's what I needed to know.
>>>
>>> Cheers,
>>>
>>> Rob
>>>
>>>
>>>
>>> From: petsc-users-bounces at mcs.anl.gov
>>> [mailto:petsc-users-bounces at mcs.anl.gov] On Behalf Of Dave May
>>> Sent: Tuesday, December 22, 2009 10:13 AM
>>> To: PETSc users list
>>> Subject: Re: [petsc-users] Two ways to set Vec values?
>>>
>>>
>>>
>>> Hey Rob
>>>   If you are sure that you only want to insert values locally into x, then
>>> option 1 will be faster.
>>> Option 2 will communicate values if the inserted values live on another
>>> processor. If you don't need to send any data, use Option 1.
>>>
>>>
>>>
>>>
>>>
>>> On Tue, Dec 22, 2009 at 7:04 PM, Rob Ellis <Robert.G.Ellis at shaw.ca> wrote:
>>>
>>> Hi Petsc'ers
>>>
>>> Can someone please let me know if I can set MPI vector values using either
>>> of the following methods? I wish to set the values of 'x' from the  
>>>  values in
>>> 'work'. Both methods operate correctly, but I would like to know which is
>>> more efficient, and/or recommended and why.
>>>
>>>
>>> 1. GetArray/RestoreArray Method:
>>>
>>> call VecGetOwnershipRange(x,imin,imax,ierr)
>>> call VecGetArray(x,x_local_v,x_local_i,ierr)
>>> do i=imin,imax-1
>>> x_local(i-imin)=work(i+1)
>>> enddo
>>> call VecRestoreArray(x,x_local_v,x_local_i,ierr)
>>>
>>>
>>>
>>> 2. SetValues/VecAssembly Method:
>>>
>>> call VecGetOwnershipRange(x,imin,imax,ierr)
>>> nx_local = imax-imin
>>> do i=imin,imax-1
>>> icol(i-imin+1)=i
>>> enddo
>>> call VecSetValues(x,nx_local,icol,work(imin+1),INSERT_VALUES,ierr)
>>> call VecAssemblyBegin(x,ierr)
>>> call VecAssemblyEnd(x,ierr)
>>>
>>>
>>> Method 1 is more compact and does not require the auxiliary column number
>>> vector, nor does it require the VecAssembly, however, it seems to   
>>> be what is
>>> suggested by the examples. Also, is it recommended to use VecGetArrayF90?
>>>
>>> Thanks for your help,
>>> Cheers,
>>> Rob
>>>
>>>
>>>
>>>
>>
>>
>>
>> -- 
>> Jarunan Panyasantisuk
>> Development Engineer
>> ASCOMP GmbH, Technoparkstr. 1
>> CH-8005 Zurich, Switzerland
>> Phone : +41 44 445 4072
>> Fax   : +41 44 445 4075
>> E-mail: jarunan at ascomp.ch
>> www.ascomp.ch
>>
>> Winter Training on TransAT: Zurich, 20 Feb. 2010.
>> http://ascomp.ch/training.html



-- 
Jarunan Panyasantisuk
Development Engineer
ASCOMP GmbH, Technoparkstr. 1
CH-8005 Zurich, Switzerland
Phone : +41 44 445 4072
Fax   : +41 44 445 4075
E-mail: jarunan at ascomp.ch
www.ascomp.ch

Winter Training on TransAT: Zurich, 20 Feb. 2010.
http://ascomp.ch/training.html