Need to scatter from a few of the processors only to the zero processor

[Randall Mackie]

At the end of my large 3D computation, I compute the results at, say, 20 locations
in the entire 3D volume. This calculation doesn't happen on every processor, but
only those processors that own that part of the 3D volume.

I want to get those results to the zero processor for output, but I'm unsure
about the best way to do this. My question is can I define a parallel vector
that is smaller than the number of processors, or does that even make sense?

Right now, I'm doing the following, and I'm wondering how to do this with
VecCreateMPI and scattering the results to the zero processor:

!
! See if computation point is owned by this processor:
!
         IF (ii >= xs .and. ii <= xs+xm-1 .and.
      .      jj >= ys .and. jj <= ys+ym-1 .and.
      .      kk >= zs .and. kk <= zs+zm-1 ) THEN

           flg=.true.

           hyijk=xh(idx+3*row+2)
           hyijf=xh(idx+3*(row+gxm*gym)+2)
           hzijk=xh(idx+3*row+3)
           hziek=xh(idx+3*(row+gxm)+3)

etc, do some computations

	END IF

         IF (flg .and. rank /= 0) THEN

           call MPI_Send(esxInterp(iTx,1), 1, MPI_DOUBLE_COMPLEX, 0, 1,
      .                  MPI_COMM_WORLD, ierr)

         ELSE IF (.not. flg .and. rank == 0) THEN

           call MPI_Recv(esxInterp(iTx,1), 1, MPI_DOUBLE_COMPLEX,
      .         MPI_ANY_SOURCE, 1, PETSC_COMM_WORLD, mpi_status, ierr)

         END IF


-- 
Randall Mackie
GSY-USA, Inc.
PMB# 643
2261 Market St.,
San Francisco, CA 94114-1600
Tel (415) 469-8649
Fax (415) 469-5044

California Registered Geophysicist
License No. GP 1034