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!
! Copyright (C) 2012 Quantum ESPRESSO group
! This file is distributed under the terms of the
! GNU General Public License. See the file `License'
! in the root directory of the present distribution,
! or http://www.gnu.org/copyleft/gpl.txt .
!
!
!-----------------------------------------------------------------------
SUBROUTINE divide (comm, ntodiv, startn, lastn)
!-----------------------------------------------------------------------
!
! Given "ntodiv" objects, distribute index across a group of processors
! belonging to communicator "comm"
! Each processor gets index from "startn" to "lastn"
! If the number of processors nproc exceeds the number of objects,
! the last nproc-ntodiv processors return startn = ntodiv+1 > lastn = ntodiv
!
USE mp, ONLY : mp_size, mp_rank
IMPLICIT NONE
!
INTEGER, INTENT(in) :: comm
! communicator
INTEGER, INTENT(in) :: ntodiv
! index to be distributed
INTEGER, INTENT(out):: startn, lastn
! indices for this processor: from startn to lastn
!
INTEGER :: me_comm, nproc_comm
! identifier of current processor
! number of processors
!
INTEGER :: ndiv, rest
! number of points per processor
! number of processors having one more points
!
nproc_comm = mp_size(comm)
me_comm = mp_rank(comm)
!
rest = mod ( ntodiv, nproc_comm )
ndiv = int( ntodiv / nproc_comm )
!
IF (rest > me_comm) THEN
startn = me_comm * (ndiv+1) + 1
lastn = (me_comm+1) * (ndiv+1)
ELSE
startn= me_comm * ndiv + rest + 1
lastn = (me_comm+1) * ndiv + rest
ENDIF
RETURN
END SUBROUTINE divide
SUBROUTINE divide_all (comm, ntodiv, startn, lastn, counts, displs)
!-----------------------------------------------------------------------
!
! Given "ntodiv" objects, distribute index across a group of processors
! belonging to communicator "comm"
! Each processor gets index from "startn" to "lastn"
! If the number of processors nproc exceeds the number of objects,
! the last nproc-ntodiv processors return startn = ntodiv+1 > lastn = ntodiv
!
USE mp, ONLY : mp_size, mp_rank
IMPLICIT NONE
!
INTEGER, INTENT(in) :: comm
! communicator
INTEGER, INTENT(in) :: ntodiv
! index to be distributed
INTEGER, INTENT(out):: startn, lastn
! indices for this processor: from startn to lastn
INTEGER, INTENT(out):: counts(*), displs(*)
! indice counts and displacements of all ranks
!
INTEGER :: me_comm, nproc_comm
! identifier of current processor
! number of processors
!
INTEGER :: ndiv, rest
! number of points per processor
! number of processors having one more points
INTEGER :: ip
!
nproc_comm = mp_size(comm)
me_comm = mp_rank(comm)
!
rest = mod ( ntodiv, nproc_comm )
ndiv = int( ntodiv / nproc_comm )
!
DO ip = 1, nproc_comm
IF (rest >= ip) THEN
counts(ip) = ndiv + 1
displs(ip) = (ip-1) * (ndiv+1)
ELSE
counts(ip) = ndiv
displs(ip) = (ip-1) * ndiv + rest
ENDIF
ENDDO
! seting startn and lastn
startn = displs(me_comm+1) + 1
lastn = displs(me_comm+1) + counts(me_comm+1)
RETURN
END SUBROUTINE divide_all
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