PRACE NPT

      Function dddot3( k, partcomm, n, x, y )          Result( dotres )

! ---------------------------------------------------------------------

      Use                   dist_module

      Use                   numerics

      Implicit              None 

      Integer            :: k, n, partcomm

      Real(l_)           :: x(n), y(n), dotres

      Include               'mpif.h'

      Integer           :: datype, ierr

      Integer           :: i

      Real(l_)          :: s

! ---------------------------------------------------------------------

! --- Do local part of dotproduct.

      s = 0.0_l_

      Do i = 1, n

         s = s + x(i)*y(i)

      End Do

      dotres = s

! ---------------------------------------------------------------------

! --- If on 1 processor we are done: Return.

      If ( k == 1 ) Return

! ---------------------------------------------------------------------

! --- Send partial results from all processors in communicator 

!     partcomm to processor 1.

      datype = MPI_Real8

      Call MPI_Reduce( s, dotres, 1, datype, MPI_Sum, 0,

     &                               partcomm, ierr )

! ---------------------------------------------------------------------

! --- Send sum to all processors in communicator partcomm.

      If ( me < k ) Call MPI_Bcast( dotres, 1, datype, 0, partcomm,

     &                              ierr )

! ---------------------------------------------------------------------

      End Function dddot3