!!$ 
!!$              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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!!$  
!
! Purpose: 
!  Provide a set of subroutines to define a data distribution based on 
!  a graph partitioning routine from METIS. May serve as the basis
!  for interfacing other graph partitioning tools.
! 
!  Subroutines:
!  
!  BUILD_MTPART(A,NPARTS): This subroutine will be called by the root
!    process to build define the data distribuition mapping. 
!      Input parameters:
!        TYPE(D_SPMAT) :: A   The input matrix. The coefficients are
!                             ignored; only the structure is used.
!        INTEGER       :: NPARTS  How many parts we are requiring to the 
!                                 partition utility
! 
!  DISTR_MTPART(RROOT,CROOT,ICTXT): This subroutine will be called by
!      all processes to distribute the information computed by the root
!      process, to be used subsequently.
!
!
!  PART_GRAPH : The subroutine to be passed to PSBLAS sparse library;
!      uses information prepared by the previous two subroutines.
!
module psb_metispart_mod
  public part_graph, build_mtpart, distr_mtpart,&
       & getv_mtpart, free_part
  private 
  integer, allocatable, save :: graph_vect(:)
  
contains
  
  subroutine part_graph(global_indx,n,np,pv,nv)
    
    integer, intent(in)  :: global_indx, n, np
    integer, intent(out) :: nv
    integer, intent(out) :: pv(*)
    
    IF (.not.allocated(graph_vect)) then
       write(0,*) 'Fatal error in PART_GRAPH: vector GRAPH_VECT ',&
	    & 'not initialized'
       return
    endif
    if ((global_indx<1).or.(global_indx > size(graph_vect))) then       
       write(0,*) 'Fatal error in PART_GRAPH: index GLOBAL_INDX ',&
	    & 'outside GRAPH_VECT bounds',global_indx,size(graph_vect)
       return
    endif
    nv = 1
    pv(nv) = graph_vect(global_indx)
    return
  end subroutine part_graph


  subroutine distr_mtpart(root, ictxt)
    use psb_base_mod
    integer    :: root, ictxt
    integer    :: n, me, np

    call psb_info(ictxt,me,np)

    if (.not.((root>=0).and.(root<np))) then 
      write(0,*) 'Fatal error in DISTR_MTPART: invalid ROOT  ',&
           & 'coordinates '
      call psb_abort(ictxt)
      return
    endif

    if (me == root) then 
      if (.not.allocated(graph_vect)) then
        write(0,*) 'Fatal error in DISTR_MTPART: vector GRAPH_VECT ',&
             & 'not initialized'
        call psb_abort(ictxt)
        return
      endif
      n = size(graph_vect)
      call psb_bcast(ictxt,n,root=root)
    else 
      call psb_bcast(ictxt,n,root=root)

      allocate(graph_vect(n),stat=info)
      if (info /= 0) then
        write(0,*) 'Fatal error in DISTR_MTPART: memory allocation ',&
             & ' failure.'
        return
      endif
    endif
    call psb_bcast(ictxt,graph_vect(1:n),root=root)

    return

  end subroutine distr_mtpart
  
  subroutine  getv_mtpart(ivg)
    integer, allocatable, intent(out)  :: ivg(:)
    if (allocated(graph_vect)) then 
      allocate(ivg(size(graph_vect)))
      ivg(:) = graph_vect(:)
    end if
  end subroutine getv_mtpart
  

  subroutine build_mtpart(n,fida,ia1,ia2,nparts)
    use psb_base_mod
    integer       :: nparts
    integer       :: ia1(:), ia2(:)
    integer       :: n, i,numflag,nedc,wgflag
    character(len=5)     :: fida
    integer, parameter :: nb=512
    real(kind(1.d0)), parameter :: seed=12345.d0
    integer          :: iopt(10),idummy(2),jdummy(2)

#if defined(HAVE_METIS)
    interface 
      subroutine METIS_PartGraphRecursive(n,ixadj,iadj,ivwg,iajw,&
           & wgflag,numflag,nparts,iopt,nedc,part)
        integer :: n,wgflag,numflag,nparts,nedc
        integer :: ixadj(*),iadj(*),ivwg(*),iajw(*),iopt(*),part(*)
      end subroutine METIS_PartGraphRecursive
    end interface    
    
    allocate(graph_vect(n),stat=info)
    
    if (info /= 0) then
       write(0,*) 'Fatal error in BUILD_MTPART: memory allocation ',&
	    & ' failure.'
       return
    endif
    if (nparts > 1) then
      if (toupper(fida) == 'CSR') then 
        iopt(1) = 0
        numflag  = 1
        wgflag   = 0

        call METIS_PartGraphRecursive(n,ia2,ia1,idummy,jdummy,&
             & wgflag,numflag,nparts,iopt,nedc,graph_vect)

        do i=1, n
          graph_vect(i) = graph_vect(i) - 1
        enddo
      else
        write(0,*) 'Fatal error in BUILD_MTPART: matrix format ',&
             & ' failure. ', FIDA
        return
      endif
    else
      do i=1, n
        graph_vect(i) = 0
      enddo
    endif
#else
    write(0,*) 'Warning: METIS was not configured at PSBLAS compile time !'
#endif

    return

  end subroutine build_mtpart 


  subroutine free_part(info)
    integer :: info
    
    deallocate(graph_vect,stat=info)
    return
  end subroutine free_part    

end module psb_metispart_mod