psblas3/base/internals/psi_fnd_owner.f90

!!$ 
!!$              Parallel Sparse BLAS  v2.0
!!$    (C) Copyright 2006 Salvatore Filippone    University of Rome Tor Vergata
!!$                       Alfredo Buttari        University of Rome Tor Vergata
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!
! File: psi_fnd_owner.f90
!
! Subroutine: psi_fnd_owner
!   Figure out who owns  global indices. 
! 
! Arguments: 
!    nv       - integer                   Number of indices required on  the calling
!                                         process 
!    idx(:)   - integer                   Required indices on the calling process
!    iprc(:)  - integer, allocatable      Output: process identifiers for the corresponding
!                                         indices
!    desc_a   - type(psb_desc_type).    The communication descriptor.        
!    info     - integer.                  return code.
! 
subroutine psi_fnd_owner(nv,idx,iprc,desc,info)
  use psb_descriptor_type
  use psb_serial_mod
  use psb_const_mod
  use psb_error_mod
  use psb_penv_mod
  use psb_realloc_mod
  use psi_mod, psb_protect_name => psi_fnd_owner
  
  implicit none 
  integer, intent(in) :: nv
  integer, intent(in) ::  idx(:)
  integer, allocatable, intent(out) ::  iprc(:)
  type(psb_desc_type), intent(in) :: desc
  integer, intent(out) :: info


  integer,allocatable :: hsz(:),hidx(:),helem(:),hproc(:)

  integer          ::  i,n_row,n_col, err_act,ih,icomm,hsize
  integer             :: ictxt,np,me
  character(len=20)   :: name

  info = 0
  name = 'psi_fnd_owner'
  call psb_erractionsave(err_act)

  ictxt   = psb_cd_get_context(desc)
  icomm   = psb_cd_get_mpic(desc)
  n_row   = psb_cd_get_local_rows(desc)
  n_col   = psb_cd_get_local_cols(desc)


  ! check on blacs grid 
  call psb_info(ictxt, me, np)
  if (np == -1) then
    info = 2010
    call psb_errpush(info,name)
    goto 9999
  endif

  if (nv < 0 ) then
    info = 2010
    call psb_errpush(info,name)
    goto 9999
  endif

  if (.not.(psb_is_ok_desc(desc))) then 
    call psb_errpush(4010,name,a_err='invalid desc')
    goto 9999      
  end if

  !
  ! The basic idea is very simple. 
  ! First we figure out the total number of requests.
  Allocate(hidx(np+1),hsz(np),stat=info)
  if (info /= 0) then 
    call psb_errpush(4010,name,a_err='Allocate') 
    goto 9999      
  end if
  hsz       = 0
  hsz(me+1) = nv
  call psb_amx(ictxt,hsz,info)
  hidx(1)   = 1
  do i=1, np
    hidx(i+1) = hidx(i) + hsz(i)
  end do
  hsize = hidx(np+1)-1
  Allocate(helem(hsize),hproc(hsize),stat=info)
  if (info /= 0) then 
    call psb_errpush(4010,name,a_err='Allocate')
    goto 9999      
  end if
  ! Second we build the aggregate list of requests (with psb_amx)
  helem(:) = 0 
  ih = hidx(me+1)
  do i=1, hsz(me+1) 
    helem(ih+i-1) = idx(i) 
  end do
  call psb_amx(ictxt,helem,info)
  ! Third, we figure out locally whether we own the indices (whoever is 
  ! asking for them) and build our part of the reply (we shift process 
  !  indices so that they're 1-based)
  call psi_idx_cnv(hsize,helem,desc,info,owned=.true.)
  if (info /= 0) then 
    call psb_errpush(4010,name,a_err='psi_idx_cnv')
    goto 9999      
  end if
  
  do i=1,hsize
    if ((0< helem(i)).and. (helem(i) <= n_row))then 
      hproc(i) = me+1
    else
      hproc(i) = 0
    end if
  end do

  ! Fourth, we do a psb_amx on the replies so that we have everybody's answers
  call psb_amx(ictxt,hproc,info)

  ! Fifth, we extract the answers for our local query, and shift back the 
  ! process indices to 0-based.
  if (nv > 0) then 
    call psb_realloc(nv,iprc,info)
    ih = hidx(me+1)
    do i=1, hsz(me+1) 
      iprc(i) = hproc(ih+i-1) - 1 
    end do 
  end if
  call psb_erractionrestore(err_act)
  return

9999 continue
  call psb_erractionrestore(err_act)

  if (err_act.eq.psb_act_ret_) then
    return
  else
    call psb_error(ictxt)
  end if
  return

end subroutine psi_fnd_owner