[petsc-users] Two ways to set Vec values?

[Dave May]

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
>
>
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