[petsc-users] KSPBuildResidual

[Barry Smith]

    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