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

[Rob Ellis]

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

 

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