amg4psblas/mlprec/impl/mld_c_dec_map_bld.F90

subroutine mld_c_dec_map_bld(theta,a,desc_a,nlaggr,ilaggr,info)

  use psb_base_mod
  use mld_c_inner_mod, mld_protect_name => mld_c_dec_map_bld

  implicit none

  ! Arguments
  type(psb_cspmat_type), intent(in) :: a
  type(psb_desc_type), intent(in)    :: desc_a
  real(psb_spk_), intent(in)         :: theta
  integer, allocatable, intent(out)  :: ilaggr(:),nlaggr(:)
  integer, intent(out)               :: info

  ! Local variables
  integer, allocatable  :: ils(:), neigh(:), irow(:), icol(:)
  complex(psb_spk_), allocatable  :: val(:), diag(:)
  integer :: icnt,nlp,k,n,ia,isz,nr, naggr,i,j,m, nz
  real(psb_spk_)  :: cpling, tcl
  logical :: recovery
  integer :: debug_level, debug_unit
  integer :: ictxt,np,me,err_act
  integer :: nrow, ncol, n_ne
  character(len=20)  :: name, ch_err

  if (psb_get_errstatus() /= 0) return 
  info=psb_success_
  name = 'mld_dec_map_bld'
  call psb_erractionsave(err_act)
  debug_unit  = psb_get_debug_unit()
  debug_level = psb_get_debug_level()
  !
  ictxt=desc_a%get_context()
  call psb_info(ictxt,me,np)
  nrow  = desc_a%get_local_rows()
  ncol  = desc_a%get_local_cols()

  nr = a%get_nrows()
  allocate(ilaggr(nr),neigh(nr),stat=info)
  if(info /= psb_success_) then
    info=psb_err_alloc_request_
    call psb_errpush(info,name,i_err=(/2*nr,0,0,0,0/),&
         & a_err='integer')
    goto 9999
  end if

  allocate(diag(nr),stat=info)
  if(info /= psb_success_) then
    info=psb_err_alloc_request_
    call psb_errpush(info,name,i_err=(/nr,0,0,0,0/),&
         & a_err='complex(psb_spk_)')
    goto 9999
  end if
  call a%get_diag(diag,info)
  if(info /= psb_success_) then
    info=psb_err_from_subroutine_
    call psb_errpush(info,name,a_err='psb_sp_getdiag')
    goto 9999
  end if

  do i=1, nr
    ilaggr(i) = -(nr+1)
  end do


  ! Note: -(nr+1)  Untouched as yet
  !       -i    1<=i<=nr  Adjacent to aggregate i
  !        i    1<=i<=nr  Belonging to aggregate i
  !
  ! Phase one: group nodes together. 
  ! Very simple minded strategy. 
  ! 
  naggr = 0
  nlp   = 0
  do
    icnt = 0
    do i=1, nr 
      if (ilaggr(i) == -(nr+1)) then 
        !
        ! 1. Untouched nodes are marked >0 together 
        !    with their neighbours
        !
        icnt      = icnt + 1 
        naggr     = naggr + 1 
        ilaggr(i) = naggr

        call a%csget(i,i,nz,irow,icol,val,info)
        if (info /= psb_success_) then 
          info=psb_err_from_subroutine_
          call psb_errpush(info,name,a_err='csget')
          goto 9999
        end if

        do k=1, nz
          j = icol(k)
          if ((1<=j).and.(j<=nr).and.(i /= j)) then 
            if (abs(val(k)) > theta*sqrt(abs(diag(i)*diag(j)))) then 
              ilaggr(j) = naggr
            else 
              ilaggr(j) = -naggr
            endif
          end if
        enddo

        !
        ! 2. Untouched neighbours of these nodes are marked <0.
        !
        call a%get_neigh(i,neigh,n_ne,info,lev=2)
        if (info /= psb_success_) then 
          info=psb_err_from_subroutine_
          call psb_errpush(info,name,a_err='psb_neigh')
          goto 9999
        end if

        do n = 1, n_ne
          m = neigh(n)
          if ((1<=m).and.(m<=nr)) then
            if (ilaggr(m) == -(nr+1)) ilaggr(m) = -naggr
          endif
        enddo
      endif
    enddo
    nlp = nlp + 1 
    if (icnt == 0) exit 
  enddo
  if (debug_level >= psb_debug_outer_) then 
    write(debug_unit,*) me,' ',trim(name),&
         & ' Check 1:',count(ilaggr == -(nr+1))
  end if

  !
  ! Phase two: sweep over leftovers. 
  !
  allocate(ils(nr),stat=info) 
  if(info /= psb_success_) then
    info=psb_err_alloc_request_
    call psb_errpush(info,name,i_err=(/naggr+10,0,0,0,0/),&
         & a_err='integer')
    goto 9999
  end if

  do i=1, size(ils)
    ils(i) = 0
  end do
  do i=1, nr 
    n = ilaggr(i)
    if (n>0) then 
      if (n>naggr) then 
        info=psb_err_internal_error_
        call psb_errpush(info,name,a_err='loc_Aggregate: n > naggr 1 ?')
        goto 9999        
      else
        ils(n) = ils(n) + 1 
      end if

    end if
  end do
  if (debug_level >= psb_debug_outer_) then 
    write(debug_unit,*) me,' ',trim(name),&
         & 'Phase 1: number of aggregates ',naggr
    write(debug_unit,*) me,' ',trim(name),&
         & 'Phase 1: nodes aggregated     ',sum(ils)
  end if

  recovery=.false.
  do i=1, nr
    if (ilaggr(i) < 0) then 
      !
      ! Now some silly rule to break ties:
      ! Group with adjacent aggregate. 
      !
      isz  = nr+1
      ia   = -1
      cpling = szero
      call a%csget(i,i,nz,irow,icol,val,info)
      if (info /= psb_success_) then 
        info=psb_err_from_subroutine_
        call psb_errpush(info,name,a_err='psb_sp_getrow')
        goto 9999
      end if

      do j=1, nz
        k = icol(j)
        if ((1<=k).and.(k<=nr).and.(k /= i))  then 
          tcl = abs(val(j)) / sqrt(abs(diag(i)*diag(k)))
          if (abs(val(j)) > theta*sqrt(abs(diag(i)*diag(k)))) then 
!!$            if (tcl > theta) then 
            n = ilaggr(k) 
            if (n>0) then 
              if (n>naggr) then 
                info=psb_err_internal_error_
                call psb_errpush(info,name,a_err='loc_Aggregate: n > naggr 2 ?')
                goto 9999        
              end if

              if ((abs(val(j))>cpling) .or. &
                   & ((abs(val(j)) == cpling).and. (ils(n) < isz))) then 
!!$                if ((tcl > cpling) .or. ((tcl  == cpling).and. (ils(n) < isz))) then
                ia     = n
                isz    = ils(n)
                cpling = abs(val(j))
!!$                  cpling = tcl
              endif
            endif
          endif
        end if
      enddo

      if (ia == -1) then 
        ! At this point, the easiest thing is to start a new aggregate
        naggr          = naggr + 1
        ilaggr(i)      = naggr 
        ils(ilaggr(i)) = 1

      else

        ilaggr(i) = ia

        if (ia>naggr) then 
          info=psb_err_internal_error_
          call psb_errpush(info,name,a_err='loc_Aggregate: n > naggr ? ')
          goto 9999        
        end if
        ils(ia)  = ils(ia) + 1
      endif

    end if
  end do
  if (debug_level >= psb_debug_outer_) then 
    if (recovery) then 
      write(debug_unit,*) me,' ',trim(name),&
           & 'Had to recover from strange situation in loc_aggregate.'
      write(debug_unit,*) me,' ',trim(name),&
           & 'Perhaps an unsymmetric pattern?'
    endif
    write(debug_unit,*) me,' ',trim(name),&
         & 'Phase 2: number of aggregates ',naggr,sum(ils) 
    do i=1, naggr 
      write(debug_unit,*) me,' ',trim(name),&
           & 'Size of aggregate ',i,' :',count(ilaggr == i), ils(i)
    enddo
    write(debug_unit,*) me,' ',trim(name),&
         & maxval(ils(1:naggr))
    write(debug_unit,*) me,' ',trim(name),&
         & 'Leftovers ',count(ilaggr<0), '  in ',nlp,' loops'
  end if

  if (count(ilaggr<0) >0) then 
    info=psb_err_internal_error_
    call psb_errpush(info,name,a_err='Fatal error: some leftovers')
    goto 9999
  endif

  deallocate(ils,neigh,stat=info)
  if (info /= psb_success_) then 
    info=psb_err_alloc_dealloc_
    call psb_errpush(info,name)
    goto 9999
  end if
  if (naggr > ncol) then 
    write(0,*) name,'Error : naggr > ncol',naggr,ncol
    info=psb_err_internal_error_
    call psb_errpush(info,name,a_err='Fatal error: naggr>ncol')
    goto 9999
  end if

  call psb_realloc(ncol,ilaggr,info)
  if (info /= psb_success_) then 
    info=psb_err_from_subroutine_
    ch_err='psb_realloc'
    call psb_errpush(info,name,a_err=ch_err)
    goto 9999
  end if

  allocate(nlaggr(np),stat=info)
  if (info /= psb_success_) then 
    info=psb_err_alloc_request_
    call psb_errpush(info,name,i_err=(/np,0,0,0,0/),&
         & a_err='integer')
    goto 9999
  end if

  nlaggr(:) = 0
  nlaggr(me+1) = naggr
  call psb_sum(ictxt,nlaggr(1:np))

  call psb_erractionrestore(err_act)
  return

9999 continue
  call psb_erractionrestore(err_act)
  if (err_act.eq.psb_act_abort_) then
    call psb_error()
    return
  end if
  return

end subroutine mld_c_dec_map_bld