psblas3/base/internals/psi_ldsc_pre_halo.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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!!$  
subroutine psi_ldsc_pre_halo(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, only : psi_fnd_owner
  implicit none
  type(psb_desc_type), intent(inout) :: desc
  integer, intent(out) :: info

  integer,allocatable :: helem(:),hproc(:)
  integer,allocatable :: tmphl(:)

  integer          ::  i,j,err,np,me,lhalo,nhalo,&
       & n_col, err_act,  key, ih, nh, idx, nk,icomm,hsize
  integer             :: ictxt,n_row
  logical, parameter  :: debug=.false., debugwrt=.false.
  character(len=20)   :: name,ch_err

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

  ictxt   = psb_cd_get_context(desc)
  n_row   = psb_cd_get_local_rows(desc)
  n_col   = psb_cd_get_local_cols(desc)
  call psb_get_mpicomm(ictxt,icomm )

  ! 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 (.not.(psb_is_bld_desc(desc).and.psb_is_large_desc(desc))) then 
    write(0,*) 'Invalid input descriptor in ldsc_pre_halo'

  end if


  nk = n_col
  call psb_realloc(nk,2,desc%glb_lc,info) 
  if (info ==0) call psb_realloc(hashsize,desc%hashv,info,lb=0)
  if (info /= 0) then 
    ch_err='psb_realloc'
    call psb_errpush(info,name,a_err=ch_err)
    goto 9999
  end if

  desc%hashv(0:hashsize) = 0
  do i=1, nk
    key = desc%loc_to_glob(i)
    ih  = iand(key,hashmask) 
    desc%hashv(ih) = desc%hashv(ih) + 1
  end do
  nh = desc%hashv(0) 
  idx = 1
  do i=1, hashsize
    desc%hashv(i-1) = idx
    idx = idx + nh
    nh = desc%hashv(i)
  end do
  do i=1, nk
    key = desc%loc_to_glob(i)
    ih  = iand(key,hashmask)
    idx = desc%hashv(ih) 
    desc%glb_lc(idx,1) = key
    desc%glb_lc(idx,2) = i
    desc%hashv(ih) = desc%hashv(ih) + 1
  end do
  do i = hashsize, 1, -1 
    desc%hashv(i) = desc%hashv(i-1)
  end do
  desc%hashv(0) = 1
  do i=0, hashsize-1 
    idx = desc%hashv(i)
    nh  = desc%hashv(i+1) - desc%hashv(i) 
    if (nh > 1) then 
      call imsrx(nh,desc%glb_lc(idx,1),desc%glb_lc(idx,2),1)
    end if
  end do

  nh = (n_col-n_row)
  if (nh > 0) then 
    Allocate(helem(nh),stat=info)
    if (info /= 0) then 
      call psb_errpush(4010,name,a_err='Allocate')
      goto 9999      
    end if

    do i=1, nh
      helem(i) = desc%loc_to_glob(n_row+i)
    end do

    call psi_fnd_owner(nh,helem,hproc,desc,info)
    allocate(tmphl((3*((n_col-n_row)+1)+1)),stat=info)
    if (info /= 0) then 
      call psb_errpush(4010,name,a_err='Allocate')
      goto 9999      
    end if
    j  = 1
    do i=1,nh
      tmphl(j+0) = hproc(i)
      if (tmphl(j+0)<0) then 
        write(0,*) 'Unrecoverable error: missing proc from asb'
      end if
      tmphl(j+1) = 1
      tmphl(j+2) = n_row+i
      j          = j + 3
    end do
    tmphl(j) = -1
    lhalo = j
    nhalo = (lhalo-1)/3
  else 
    allocate(tmphl(1),stat=info) 
    if (info /= 0) then 
      call psb_errpush(4010,name,a_err='Allocate')
      goto 9999      
    end if
    tmphl=-1
  endif


  call psb_transfer(tmphl,desc%halo_index,info)

  call psb_erractionrestore(err_act)
  return

9999 continue
  call psb_erractionrestore(err_act)

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


end subroutine psi_ldsc_pre_halo