! WHIZARD 2.0.0_rc4 Wed Mar 03 2010
! 
! (C) 1999-2010 by 
!     Wolfgang Kilian <kilian@hep.physik.uni-siegen.de>
!     Thorsten Ohl <ohl@physik.uni-wuerzburg.de>
!     Juergen Reuter <juergen.reuter@physik.uni-freiburg.de>
!     with contributions by Christian Speckner, Sebastian Schmidt, 
!     Daniel Wiesler, Felix Braam
!
! WHIZARD is free software; you can redistribute it and/or modify it
! under the terms of the GNU General Public License as published by 
! the Free Software Foundation; either version 2, or (at your option)
! any later version.
!
! WHIZARD is distributed in the hope that it will be useful, but
! WITHOUT ANY WARRANTY; without even the implied warranty of
! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
! GNU General Public License for more details.
!
! You should have received a copy of the GNU General Public License
! along with this program; if not, write to the Free Software
! Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
! This file has been stripped of most comments.  For documentation, refer
! to the source 'whizard.nw'

module particles

  use kinds, only: default !NODEP!
  use iso_varying_string, string_t => varying_string !NODEP!
  use file_utils !NODEP!
  use lorentz !NODEP!
  use prt_lists
  use expressions
  use models
  use flavors
  use colors
  use helicities
  use quantum_numbers
  use state_matrices
  use interactions
  use evaluators
  use polarizations
  use event_formats
  use hepmc_interface

  implicit none
  private

  public :: particle_set_t
  public :: particle_set_init
  public :: particle_set_final
  public :: particle_set_write
  public :: particle_set_write_raw 
  public :: particle_set_read_raw 
  public :: particle_set_fill_hepeup
  public :: particle_set_fill_hepevt
  public :: particle_set_fill_hepmc_event
  public :: particle_set_reset_status
  public :: particle_set_get_n_out, particle_set_get_n_in, &
                particle_set_get_n_tot
  public :: particle_set_reduce
  public :: particle_set_to_prt_list
  public :: particles_test

  integer, parameter :: PRT_UNPOLARIZED = 0
  integer, parameter :: PRT_DEFINITE_HELICITY = 1
  integer, parameter :: PRT_GENERIC_POLARIZATION = 2

       
  type :: particle_t
     private
     integer :: status = PRT_UNDEFINED
     integer :: polarization = PRT_UNPOLARIZED
     type(flavor_t) :: flv
     type(color_t) :: col
     type(helicity_t) :: hel
     type(polarization_t) :: pol
     type(vector4_t) :: p = vector4_null
     real(default) :: p2 = 0
     integer, dimension(:), allocatable :: parent
     integer, dimension(:), allocatable :: child
  end type particle_t

  type :: particle_set_t
     private
     integer :: n_in  = 0
     integer :: n_vir = 0
     integer :: n_out = 0
     integer :: n_tot = 0
     type(particle_t), dimension(:), allocatable :: prt
     type(state_matrix_t) :: correlated_state
  end type particle_set_t


  interface particle_init
     module procedure particle_init_particle
     module procedure particle_init_state
     module procedure particle_init_hepmc
  end interface

  interface particle_set_init
     module procedure particle_set_init_interaction
     module procedure particle_set_init_hepmc
  end interface


contains

  subroutine particle_init_particle (prt_out, prt_in)
    type(particle_t), intent(out) :: prt_out
    type(particle_t), intent(in) :: prt_in
    prt_out%status = prt_in%status
    prt_out%polarization = prt_in%polarization
    prt_out%flv = prt_in%flv
    prt_out%col = prt_in%col
    prt_out%hel = prt_in%hel
    prt_out%pol = prt_in%pol
    prt_out%p = prt_in%p
    prt_out%p2 = prt_in%p2
  end subroutine particle_init_particle

  subroutine particle_init_state (prt, state, status, mode)
    type(particle_t), intent(out) :: prt
    type(state_matrix_t), intent(in) :: state
    integer, intent(in) :: status, mode
    type(state_iterator_t) :: it
    prt%status = status
    call state_iterator_init (it, state)
    prt%flv = state_iterator_get_flavor (it, 1)
    if (flavor_is_beam_remnant (prt%flv))  prt%status = PRT_BEAM_REMNANT
    prt%col = state_iterator_get_color (it, 1)
    select case (mode)
    case (FM_SELECT_HELICITY)
       prt%hel = state_iterator_get_helicity (it, 1)
       prt%polarization = PRT_DEFINITE_HELICITY
    case (FM_FACTOR_HELICITY)
       call polarization_init_state_matrix (prt%pol, state)
       prt%polarization = PRT_GENERIC_POLARIZATION
    end select
  end subroutine particle_init_state

  subroutine particle_init_hepmc (prt, hprt, model, polarization, barcode)
    type(particle_t), intent(out) :: prt
    type(hepmc_particle_t), intent(in) :: hprt
    type(model_t), intent(in), target :: model
    integer, intent(in) :: polarization
    integer, dimension(:), intent(in) :: barcode
    type(hepmc_polarization_t) :: hpol
    integer :: n_parents, n_children
    integer, dimension(:), allocatable :: parent_barcode, child_barcode
    integer :: i
    select case (hepmc_particle_get_status (hprt))
    case (1);  prt%status = PRT_OUTGOING
    case (2);  prt%status = PRT_RESONANT
    case (3);  prt%status = PRT_VIRTUAL
    end select
    call flavor_init (prt%flv, hepmc_particle_get_pdg (hprt), model)
    if (flavor_is_beam_remnant (prt%flv))  prt%status = PRT_BEAM_REMNANT
    call color_init (prt%col, hepmc_particle_get_color (hprt))
    prt%polarization = polarization
    select case (polarization)
    case (PRT_DEFINITE_HELICITY)
       hpol = hepmc_particle_get_polarization (hprt)
       call hepmc_polarization_to_hel (hpol, prt%flv, prt%hel)
       call hepmc_polarization_final (hpol)
    case (PRT_GENERIC_POLARIZATION)
       hpol = hepmc_particle_get_polarization (hprt)
       call hepmc_polarization_to_pol (hpol, prt%flv, prt%pol)
       call hepmc_polarization_final (hpol)
    end select
    prt%p = hepmc_particle_get_momentum (hprt)
    prt%p2 = hepmc_particle_get_mass_squared (hprt)
    n_parents  = hepmc_particle_get_n_parents  (hprt)
    n_children = hepmc_particle_get_n_children (hprt)
    allocate (parent_barcode (n_parents),  prt%parent (n_parents))
    allocate (child_barcode  (n_children), prt%child  (n_children))
    parent_barcode = hepmc_particle_get_parent_barcodes (hprt)
    child_barcode  = hepmc_particle_get_child_barcodes  (hprt)
    do i = 1, size (barcode)
       where (parent_barcode == barcode(i))  prt%parent = i
       where (child_barcode  == barcode(i))  prt%child  = i
    end do
    if (prt%status == PRT_VIRTUAL .and. n_parents == 0) &
         prt%status = PRT_INCOMING
  end subroutine particle_init_hepmc

  elemental subroutine particle_final (prt)
    type(particle_t), intent(inout) :: prt
    call polarization_final (prt%pol)
  end subroutine particle_final

  subroutine particle_write (prt, unit)
    type(particle_t), intent(in) :: prt
    integer, intent(in), optional :: unit
    integer :: u
    u = output_unit (unit);  if (u < 0)  return
    select case (prt%status)
    case (PRT_UNDEFINED);    write (u, "(1x, A)", advance="no")  "[-]"
    case (PRT_BEAM);         write (u, "(1x, A)", advance="no")  "[b]"
    case (PRT_INCOMING);     write (u, "(1x, A)", advance="no")  "[i]"
    case (PRT_OUTGOING);     write (u, "(1x, A)", advance="no")  "[o]"
    case (PRT_VIRTUAL);      write (u, "(1x, A)", advance="no")  "[v]"
    case (PRT_RESONANT);     write (u, "(1x, A)", advance="no")  "[r]"
    case (PRT_BEAM_REMNANT); write (u, "(1x, A)", advance="no")  "[x]"
    end select
    write (u, "(1x)", advance="no")
    call flavor_write (prt%flv, unit)
    call color_write (prt%col, unit)
    select case (prt%polarization)
    case (PRT_DEFINITE_HELICITY)
       call helicity_write (prt%hel, unit)
       write (u, *)
    case (PRT_GENERIC_POLARIZATION)
       write (u, *)
       call polarization_write (prt%pol, unit)
    case default
       write (u, *)
    end select
    write (u, *) "Momentum:"
    call vector4_write (prt%p, unit)
    write (u, "(1x,A)", advance="no")  "T = "
    write (u, *)  prt%p2
    if (allocated (prt%parent)) then
       if (size (prt%parent) /= 0) then
          write (u, "(1x,A,40(1x,I0))")  "Parents: ", prt%parent
       end if
    end if
    if (allocated (prt%child)) then
       if (size (prt%child) /= 0) then
          write (u, "(1x,A,40(1x,I0))")  "Children:", prt%child
       end if
    end if
  end subroutine particle_write

  subroutine particle_write_raw (prt, u)
    type(particle_t), intent(in) :: prt
    integer, intent(in) :: u
    write (u) prt%status, prt%polarization
    call flavor_write_raw (prt%flv, u)
    call color_write_raw (prt%col, u)
    select case (prt%polarization)
    case (PRT_DEFINITE_HELICITY)
       call helicity_write_raw (prt%hel, u)
    case (PRT_GENERIC_POLARIZATION)
       call polarization_write_raw (prt%pol, u)
    end select
    call vector4_write_raw (prt%p, u)
    write (u) prt%p2
    write (u) allocated (prt%parent)
    if (allocated (prt%parent)) then
       write (u) size (prt%parent)
       write (u) prt%parent
    end if
    write (u) allocated (prt%child)
    if (allocated (prt%child)) then
       write (u) size (prt%child)
       write (u) prt%child
    end if
  end subroutine particle_write_raw

  subroutine particle_read_raw (prt, u, iostat)
    type(particle_t), intent(out) :: prt
    integer, intent(in) :: u
    integer, intent(out), optional :: iostat
    logical :: allocated_parent, allocated_child
    integer :: size_parent, size_child
    read (u, iostat=iostat) prt%status, prt%polarization
    call flavor_read_raw (prt%flv, u, iostat=iostat)
    call color_read_raw (prt%col, u, iostat=iostat)
    select case (prt%polarization)
    case (PRT_DEFINITE_HELICITY)
       call helicity_read_raw (prt%hel, u, iostat=iostat)
    case (PRT_GENERIC_POLARIZATION)
       call polarization_read_raw (prt%pol, u, iostat=iostat)
    end select
    call vector4_read_raw (prt%p, u, iostat=iostat)
    read (u, iostat=iostat) prt%p2
    read (u, iostat=iostat) allocated_parent
    if (allocated_parent) then
       read (u, iostat=iostat) size_parent
       allocate (prt%parent (size_parent))
       read (u, iostat=iostat) prt%parent
    end if
    read (u, iostat=iostat) allocated_child
    if (allocated_child) then
       read (u, iostat=iostat) size_child
       allocate (prt%child (size_child))
       read (u, iostat=iostat) prt%child
    end if
  end subroutine particle_read_raw

  subroutine particle_to_hepmc (prt, hprt)
    type(particle_t), intent(in) :: prt
    type(hepmc_particle_t), intent(out) :: hprt
    integer :: hepmc_status
    select case (prt%status)
    case (PRT_UNDEFINED)
       hepmc_status = 0
    case (PRT_OUTGOING)
       hepmc_status = 1
    case (PRT_RESONANT)
       hepmc_status = 2
    case default
       hepmc_status = 3
    end select
    call hepmc_particle_init &
         (hprt, prt%p, flavor_get_pdg (prt%flv), hepmc_status)
    call hepmc_particle_set_color (hprt, prt%col)
    select case (prt%polarization)
    case (PRT_DEFINITE_HELICITY)
       call hepmc_particle_set_polarization (hprt, prt%hel)
    case (PRT_GENERIC_POLARIZATION)
       call hepmc_particle_set_polarization (hprt, prt%pol)
    end select
  end subroutine particle_to_hepmc

  elemental subroutine particle_reset_status (prt, status)
    type(particle_t), intent(inout) :: prt
    integer, intent(in) :: status
    prt%status = status
  end subroutine particle_reset_status

  elemental subroutine particle_set_momentum (prt, p)
    type(particle_t), intent(inout) :: prt
    type(vector4_t), intent(in) :: p
    prt%p = p
    prt%p2 = p ** 2
  end subroutine particle_set_momentum

  elemental subroutine particle_set_resonance_flag (prt, resonant)
    type(particle_t), intent(inout) :: prt
    logical, intent(in) :: resonant
    select case (prt%status)
    case (PRT_VIRTUAL)
       if (resonant)  prt%status = PRT_RESONANT
    end select
  end subroutine particle_set_resonance_flag

  subroutine particle_boost_decay_momenta (pset)
    type(particle_set_t), intent(inout), target :: pset
    type(particle_t), pointer :: prt, mprt
    integer, dimension(1) :: i_mother
    integer :: i
    type(vector4_t) :: prest, pmother
    real(default) :: mass
    do i=1,pset%n_tot
       prt => pset%prt(i)
       if (particle_get_n_parents (prt) == 1) then
          i_mother = particle_get_parents (prt)
          mprt => pset%prt(i_mother(1))
          if (mprt%status == PRT_RESONANT) then
             prest = particle_get_momentum(prt)
             pmother = particle_get_momentum(mprt)
             mass = flavor_get_mass(mprt%flv)
             prt%p = boost(pmother,mass)*prest
          end if
       end if
    end do
  end subroutine particle_boost_decay_momenta

  subroutine particle_set_children (prt, idx)
    type(particle_t), intent(inout) :: prt
    integer, dimension(:), intent(in) :: idx
    if (allocated (prt%child))  deallocate (prt%child)
    allocate (prt%child (count (idx /= 0)))
    prt%child = pack (idx, idx /= 0)
  end subroutine particle_set_children

  subroutine particle_set_parents (prt, idx)
    type(particle_t), intent(inout) :: prt
    integer, dimension(:), intent(in) :: idx
    if (allocated (prt%parent))  deallocate (prt%parent) 
    allocate (prt%parent (count (idx /= 0)))
    prt%parent = pack (idx, idx /= 0)
  end subroutine particle_set_parents

  elemental function particle_get_status (prt) result (status)
    integer :: status
    type(particle_t), intent(in) :: prt
    status = prt%status
  end function particle_get_status

  elemental function particle_is_real (prt, keep_beams) result (flag)
    logical :: flag, kb
    type(particle_t), intent(in) :: prt
    logical, intent(in), optional :: keep_beams
    kb = .false.
    if (present (keep_beams)) kb = keep_beams
    select case (prt%status)
    case (PRT_INCOMING, PRT_OUTGOING, PRT_RESONANT)
       flag = .true.
    case (PRT_BEAM)
       flag = kb 
    case default
       flag = .false.
    end select
  end function particle_is_real

  elemental function particle_get_polarization_status (prt) result (status)
    integer :: status
    type(particle_t), intent(in) :: prt
    status = prt%polarization
  end function particle_get_polarization_status

  elemental function particle_get_pdg (prt) result (pdg)
    integer :: pdg
    type(particle_t), intent(in) :: prt
    pdg = flavor_get_pdg (prt%flv)
  end function particle_get_pdg

  function particle_get_color (prt) result (col)
    integer, dimension(2) :: col
    type(particle_t), intent(in) :: prt
    col(1) = color_get_col (prt%col)
    col(2) = color_get_acl (prt%col)
  end function particle_get_color
  
  function particle_get_polarization (prt) result (pol)
    type(polarization_t) :: pol
    type(particle_t), intent(in) :: prt
    pol = prt%pol
  end function particle_get_polarization

  function particle_get_helicity (prt) result (hel)
    integer :: hel
    integer, dimension(2) :: hel_arr
    type(particle_t), intent(in) :: prt    
    hel = 0
    if (helicity_is_defined (prt%hel) .and. &
        helicity_is_diagonal (prt%hel)) then
        hel_arr = helicity_get (prt%hel)
        hel = hel_arr (1)
    end if
  end function particle_get_helicity  
  
  function particle_get_n_parents (prt) result (n)
    integer :: n
    type(particle_t), intent(in) :: prt
    if (allocated (prt%parent)) then
       n = size (prt%parent)
    else
       n = 0
    end if
  end function particle_get_n_parents
    
  function particle_get_n_children (prt) result (n)
    integer :: n
    type(particle_t), intent(in) :: prt
    if (allocated (prt%child)) then
       n = size (prt%child)
    else
       n = 0
    end if
  end function particle_get_n_children
    
  function particle_get_parents (prt) result (parent)
    type(particle_t), intent(in) :: prt
    integer, dimension(:), allocatable :: parent
    if (allocated (prt%parent)) then
       allocate (parent (size (prt%parent)))
       parent = prt%parent
    else
       allocate (parent (0))
    end if
  end function particle_get_parents

  function particle_get_children (prt) result (child)
    type(particle_t), intent(in) :: prt
    integer, dimension(:), allocatable :: child
    if (allocated (prt%child)) then
       allocate (child (size (prt%child)))
       child = prt%child
    else
       allocate (child (0))
    end if
  end function particle_get_children

  function particle_get_momentum (prt) result (p)
    type(vector4_t) :: p
    type(particle_t), intent(in) :: prt
    p = prt%p
  end function particle_get_momentum

  function particle_get_p2 (prt) result (p2)
    real(default) :: p2
    type(particle_t), intent(in) :: prt
    p2 = prt%p2
  end function particle_get_p2

  subroutine particle_set_init_interaction &
       (particle_set, int, int_flows, mode, x, &
        keep_correlations, keep_virtual, n_incoming)
    type(particle_set_t), intent(out) :: particle_set
    type(interaction_t), intent(in), target :: int, int_flows
    integer, intent(in) :: mode
    real(default), dimension(2), intent(in) :: x
    logical, intent(in) :: keep_correlations, keep_virtual
    integer, intent(in), optional :: n_incoming
    type(state_matrix_t), dimension(:), allocatable, target :: flavor_state
    type(state_matrix_t), dimension(:), allocatable, target :: single_state
    integer :: n_in, n_vir, n_out, n_tot
    type(quantum_numbers_t), dimension(:,:), allocatable :: qn
    integer :: i, j
    if (present (n_incoming)) then
       n_in  = n_incoming
       n_vir = interaction_get_n_vir (int) - n_incoming
    else
       n_in  = interaction_get_n_in  (int)
       n_vir = interaction_get_n_vir (int)
    end if
    n_out = interaction_get_n_out (int)
    n_tot = interaction_get_n_tot (int)
    particle_set%n_in  = n_in
    particle_set%n_out = n_out
    if (keep_virtual) then
       particle_set%n_vir = n_vir
       particle_set%n_tot = n_tot
    else
       particle_set%n_vir = 0
       particle_set%n_tot = n_in + n_out
    end if
    call interaction_factorize (int, FM_IGNORE_HELICITY, x(1), flavor_state)
    allocate (qn (n_tot,1))
    do i = 1, n_tot
       qn(i,:) = state_matrix_get_quantum_numbers (flavor_state(i), 1)
    end do
    if (keep_correlations .and. keep_virtual) then
       call interaction_factorize (int_flows, &
            mode, x(2), single_state, particle_set%correlated_state, qn(:,1))
    else
       call interaction_factorize (int_flows, &
            mode, x(2), single_state, qn_in=qn(:,1))
    end if
    allocate (particle_set%prt (particle_set%n_tot))
    j = 1
    do i = 1, n_tot
       if (i <= n_in) then
          call particle_init &
               (particle_set%prt(j), single_state(i), PRT_INCOMING, mode)
       else if (i <= n_in + n_vir) then
          if (.not. keep_virtual)  cycle
          call particle_init &
               (particle_set%prt(j), single_state(i), PRT_VIRTUAL, mode) 
       else
          call particle_init &
               (particle_set%prt(j), single_state(i), PRT_OUTGOING, mode)
       end if
       call particle_set_momentum &
            (particle_set%prt(j), interaction_get_momentum (int, i))
       if (keep_virtual) then
          call particle_set_children &
               (particle_set%prt(j), interaction_get_children (int, i))
          call particle_set_parents &
               (particle_set%prt(j), interaction_get_parents (int, i))
       end if
       j = j + 1
    end do
    if (keep_virtual) then
       call particle_set_resonance_flag &
            (particle_set%prt, interaction_get_resonance_flags (int))
    end if
    call particle_boost_decay_momenta (particle_set)
    call state_matrix_final (flavor_state)
    call state_matrix_final (single_state)
  end subroutine particle_set_init_interaction

  subroutine particle_set_init_hepmc (particle_set, evt, model, polarization)
    type(particle_set_t), intent(out) :: particle_set
    type(hepmc_event_t), intent(in) :: evt
    type(model_t), intent(in), target :: model
    integer, intent(in) :: polarization
    type(hepmc_event_particle_iterator_t) :: it
    type(hepmc_particle_t) :: prt
    integer, dimension(:), allocatable :: barcode
    integer :: n_tot, i
    n_tot = 0
    call hepmc_event_particle_iterator_init (it, evt)
    do while (hepmc_event_particle_iterator_is_valid (it))
       n_tot = n_tot + 1
       call hepmc_event_particle_iterator_advance (it)
    end do
    allocate (barcode (n_tot))
    call hepmc_event_particle_iterator_reset (it)
    do i = 1, n_tot
       barcode(i) = hepmc_particle_get_barcode &
            (hepmc_event_particle_iterator_get (it))
       call hepmc_event_particle_iterator_advance (it)
    end do
    allocate (particle_set%prt (n_tot))
    call hepmc_event_particle_iterator_reset (it)
    do i = 1, n_tot
       prt = hepmc_event_particle_iterator_get (it)
       call particle_init (particle_set%prt(i), &
            prt, model, polarization, barcode)
       call hepmc_event_particle_iterator_advance (it)
    end do
    call hepmc_event_particle_iterator_final (it)
    particle_set%n_tot = n_tot
  end subroutine particle_set_init_hepmc

  subroutine particle_set_final (particle_set)
    type(particle_set_t), intent(inout) :: particle_set
    if (allocated (particle_set%prt))  call particle_final (particle_set%prt)
    call state_matrix_final (particle_set%correlated_state)
  end subroutine particle_set_final

  subroutine particle_set_write (particle_set, unit)
    type(particle_set_t), intent(in) :: particle_set
    integer, intent(in), optional :: unit
    integer :: u, i
    u = output_unit (unit);  if (u < 0)  return
    write (u, "(1x,A)") "Particle set:"
    if (particle_set%n_tot /= 0) then
       do i = 1, particle_set%n_tot
          write (u, "(1x,A,1x,I0)", advance="no") "Particle", i
          call particle_write (particle_set%prt(i), u)
       end do
       if (state_matrix_is_defined (particle_set%correlated_state)) then
          write (u, *) "Correlated state density matrix:"
          call state_matrix_write (particle_set%correlated_state, u)
       end if
    else
       write (u, "(3x,A)") "[empty]"
    end if
  end subroutine particle_set_write

  subroutine particle_set_write_raw (particle_set, u)
    type(particle_set_t), intent(in) :: particle_set
    integer, intent(in) :: u
    integer :: i
    write (u) particle_set%n_in, particle_set%n_vir, particle_set%n_out
    write (u) particle_set%n_tot
    do i = 1, particle_set%n_tot
       call particle_write_raw (particle_set%prt(i), u)
    end do
    call state_matrix_write_raw (particle_set%correlated_state, u)
  end subroutine particle_set_write_raw

  subroutine particle_set_read_raw (particle_set, u, iostat)
    type(particle_set_t), intent(out) :: particle_set
    integer, intent(in) :: u
    integer, intent(out), optional :: iostat
    integer :: i
    read (u, iostat=iostat) &
         particle_set%n_in, particle_set%n_vir, particle_set%n_out
    read (u, iostat=iostat) particle_set%n_tot
    allocate (particle_set%prt (particle_set%n_tot))
    do i = 1, size (particle_set%prt)
       call particle_read_raw (particle_set%prt(i), u, iostat=iostat)
    end do
    call state_matrix_read_raw (particle_set%correlated_state, u, iostat=iostat)
  end subroutine particle_set_read_raw

  subroutine particle_set_fill_hepeup (particle_set)
    type(particle_set_t), intent(in), target :: particle_set
    type(particle_t), pointer :: prt
    type(particle_set_t), target :: pset_reduced
    integer :: i, n_parents
    integer, dimension(1) :: i_mother
    call particle_set_reduce (particle_set, pset_reduced)
    call hepeup_init (pset_reduced%n_tot)
    do i = 1, pset_reduced%n_tot
       prt => pset_reduced%prt(i)
       call hepeup_set_particle (i, &
            particle_get_pdg (prt), &
            particle_get_status (prt), &
            particle_get_parents (prt), &
            particle_get_color (prt), &
            particle_get_momentum (prt), &
            particle_get_p2 (prt))
       n_parents = particle_get_n_parents (prt)
       if (n_parents == 1) then
          i_mother = particle_get_parents (prt)
          select case (particle_get_polarization_status (prt))
          case (PRT_GENERIC_POLARIZATION)
             call hepeup_set_particle_spin (i, &
                  particle_get_momentum (prt), &
                  particle_get_polarization (prt), &
                  particle_get_momentum (pset_reduced%prt(i_mother(1))))
          end select
       end if
    end do
    call particle_set_final (pset_reduced)
  end subroutine particle_set_fill_hepeup

  subroutine particle_set_fill_hepevt (particle_set, keep_beams)
    type(particle_set_t), intent(in), target :: particle_set
    type(particle_t), pointer :: prt
    type(particle_set_t), target :: pset_reduced
    logical, intent(in), optional :: keep_beams
    logical :: kb
    integer :: i, n_parents
    integer, dimension(1) :: i_mother
    kb = .false.
    if (present (keep_beams)) kb = keep_beams
    call particle_set_reduce (particle_set, pset_reduced, kb)
    call hepevt_init (pset_reduced%n_tot, pset_reduced%n_out)    
    do i = 1, pset_reduced%n_tot
       prt => pset_reduced%prt(i)
       call hepevt_set_particle (i, &
            particle_get_pdg (prt), &
            particle_get_status (prt), &
            particle_get_parents (prt), &
            particle_get_children (prt), &
            particle_get_momentum (prt), &
            particle_get_p2 (prt), &
            particle_get_helicity (prt))
    end do
    call particle_set_final (pset_reduced)
  end subroutine particle_set_fill_hepevt

  subroutine particle_set_fill_hepmc_event (particle_set, evt)
    type(particle_set_t), intent(in) :: particle_set
    type(hepmc_event_t), intent(inout) :: evt
    type(hepmc_vertex_t), dimension(:), allocatable :: v
    type(hepmc_particle_t), dimension(:), allocatable :: hprt
    integer, dimension(:), allocatable :: v_from, v_to
    integer :: n_vertices, i
    allocate (v_from (particle_set%n_tot), v_to (particle_set%n_tot))
    call particle_set_assign_vertices (particle_set, v_from, v_to, n_vertices)
    allocate (v (n_vertices))
    do i = 1, n_vertices
       call hepmc_vertex_init (v(i))
       call hepmc_event_add_vertex (evt, v(i))
    end do
    allocate (hprt (particle_set%n_tot))
    do i = 1, particle_set%n_tot
       if (v_to(i) /= 0 .or. v_from(i) /= 0) then
          call particle_to_hepmc (particle_set%prt(i), hprt(i))
       end if
    end do
    do i = 1, particle_set%n_tot
       if (v_to(i) /= 0) then
          call hepmc_vertex_add_particle_in (v(v_to(i)), hprt(i))
       end if
    end do
    do i = 1, particle_set%n_tot
       if (v_from(i) /= 0) then
          call hepmc_vertex_add_particle_out (v(v_from(i)), hprt(i))
       end if
    end do
  end subroutine particle_set_fill_hepmc_event
  
  subroutine particle_set_reset_status (particle_set, index, status)
    type(particle_set_t), intent(inout) :: particle_set
    integer, dimension(:), intent(in) :: index
    integer, intent(in) :: status
    integer :: i
    if (allocated (particle_set%prt)) then
       do i = 1, size (index)
          call particle_reset_status (particle_set%prt(index(i)), status)
       end do
    end if
  end subroutine particle_set_reset_status

  function particle_set_get_real_parents (pset, i, keep_beams) result (parent)
    integer, dimension(:), allocatable :: parent
    type(particle_set_t), intent(in) :: pset
    integer, intent(in) :: i
    logical, intent(in), optional :: keep_beams
    logical, dimension(:), allocatable :: is_real
    logical, dimension(:), allocatable :: is_parent, is_real_parent
    logical :: kb
    integer :: j, k
    kb = .false.
    if (present (keep_beams)) kb = keep_beams
    allocate (is_real (pset%n_tot))
    is_real = particle_is_real (pset%prt(i), kb)
    allocate (is_parent (pset%n_tot), is_real_parent (pset%n_tot))
    is_real_parent = .false.
    is_parent = .false.
    is_parent(particle_get_parents(pset%prt(i))) = .true.
    do while (any (is_parent))
       where (is_real .and. is_parent)
          is_real_parent = .true.
          is_parent = .false.
       end where
       do j = size (is_parent), 1, -1
          if (is_parent(j)) then
             is_parent(particle_get_parents(pset%prt(j))) = .true.
          end if
       end do
    end do
    allocate (parent (count (is_real_parent)))
    j = 0
    do k = 1, size (is_parent)
       if (is_real_parent(k)) then
          j = j + 1
          parent(j) = k
       end if
    end do
  end function particle_set_get_real_parents

  function particle_set_get_real_children (pset, i, keep_beams) result (child)
    integer, dimension(:), allocatable :: child
    type(particle_set_t), intent(in) :: pset
    integer, intent(in) :: i
    logical, dimension(:), allocatable :: is_real
    logical, dimension(:), allocatable :: is_child, is_real_child
    logical, intent(in), optional :: keep_beams
    integer :: j, k
    logical :: kb
    kb = .false.
    if (present (keep_beams)) kb = keep_beams
    allocate (is_real (pset%n_tot))
    is_real = particle_is_real (pset%prt(i), kb)
    allocate (is_child (pset%n_tot), is_real_child (pset%n_tot))
    is_real_child = .false.
    is_child = .false.
    is_child(particle_get_children(pset%prt(i))) = .true.
    do while (any (is_child))
       where (is_real .and. is_child)
          is_real_child = .true.
          is_child = .false.
       end where
       do j = 1, size (is_child)
          if (is_child(j)) then
             is_child(particle_get_children(pset%prt(j))) = .true.
          end if
       end do
    end do
    allocate (child (count (is_real_child)))
    j = 0
    do k = 1, size (is_child)
       if (is_real_child(k)) then
          j = j + 1
          child(j) = k
       end if
    end do
  end function particle_set_get_real_children

  function particle_set_get_n_out (pset) result (n_out)
     type(particle_set_t), intent(in) :: pset
     integer :: n_out
     n_out = pset%n_out
  end function particle_set_get_n_out
  
  function particle_set_get_n_in (pset) result (n_in)
     type(particle_set_t), intent(in) :: pset
     integer :: n_in
     n_in = pset%n_in
  end function particle_set_get_n_in

  function particle_set_get_n_tot (pset) result (n_tot)
     type(particle_set_t), intent(in) :: pset
     integer :: n_tot
     n_tot = pset%n_tot
  end function particle_set_get_n_tot

  subroutine particle_set_reduce (pset_in, pset_out, keep_beams)
    type(particle_set_t), intent(in) :: pset_in
    type(particle_set_t), intent(out) :: pset_out
    logical, intent(in), optional :: keep_beams
    integer, dimension(:), allocatable :: status, map
    integer :: i, j
    logical :: kb
    kb = .false.
    if (present (keep_beams)) kb = keep_beams
    allocate (status (pset_in%n_tot))    
    status = particle_get_status (pset_in%prt)
    if (kb) then 
       pset_out%n_in  = count (status == PRT_BEAM)
       pset_out%n_vir = count (status == PRT_INCOMING) &
            + count (status == PRT_RESONANT)
    else            
       pset_out%n_in  = count (status == PRT_INCOMING)
       pset_out%n_vir = count (status == PRT_RESONANT)
    end if 
    pset_out%n_out = count (status == PRT_OUTGOING)
    pset_out%n_tot = pset_out%n_in + pset_out%n_vir + pset_out%n_out
    allocate (pset_out%prt (pset_out%n_tot))
    allocate (map (pset_in%n_tot))
    map = 0
    j = 0
    if (kb) call copy_particles (PRT_BEAM)
    call copy_particles (PRT_INCOMING)
    call copy_particles (PRT_RESONANT)
    call copy_particles (PRT_OUTGOING)
    do i = 1, pset_in%n_tot
       if (map(i) == 0)  cycle
! triggers nagfor bug!
!        call particle_set_parents (pset_out%prt(map(i)), &
!             map (particle_set_get_real_parents (pset_in, i)))
!        call particle_set_children (pset_out%prt(map(i)), &
!             map (particle_set_get_real_children (pset_in, i)))
! workaround:
       call particle_set_parents (pset_out%prt(map(i)), &
            particle_set_get_real_parents (pset_in, i, kb))
       call particle_set_parents (pset_out%prt(map(i)), &
            map (pset_out%prt(map(i))%parent))
       call particle_set_children (pset_out%prt(map(i)), &
            particle_set_get_real_children (pset_in, i, kb))
       call particle_set_children (pset_out%prt(map(i)), &
            map (pset_out%prt(map(i))%child))
    end do
  contains
    subroutine copy_particles (stat)
      integer, intent(in) :: stat
      integer :: i
      do i = 1, pset_in%n_tot
         if (status(i) == stat) then
            j = j + 1
            map(i) = j
            call particle_init (pset_out%prt(j), pset_in%prt(i))
         end if
      end do
    end subroutine copy_particles
  end subroutine particle_set_reduce

  subroutine particle_set_assign_vertices &
       (particle_set, v_from, v_to, n_vertices)
    type(particle_set_t), intent(in) :: particle_set
    integer, dimension(:), intent(out) :: v_from, v_to
    integer, intent(out) :: n_vertices
    integer, dimension(:), allocatable :: parent, child
    integer :: n_parents, n_children, vf, vt
    integer :: i, j, v
    v_from = 0
    v_to = 0
    vf = 0
    vt = 0
    do i = 1, particle_set%n_tot
       n_parents = particle_get_n_parents (particle_set%prt(i))
       if (n_parents /= 0) then
          allocate (parent (n_parents))
          parent = particle_get_parents (particle_set%prt(i))
          SCAN_PARENTS: do j = 1, size (parent)
             v = v_to(parent(j))
             if (v /= 0) then
                v_from(i) = v;  exit SCAN_PARENTS
             end if
          end do SCAN_PARENTS
          if (v_from(i) == 0) then
             vf = vf + 1;  v_from(i) = vf
             v_to(parent) = vf
          end if
          deallocate (parent)
       end if
       n_children = particle_get_n_children (particle_set%prt(i))
       if (n_children /= 0) then
          allocate (child (n_children))
          child = particle_get_children (particle_set%prt(i))
          SCAN_CHILDREN: do j = 1, size (child)
             v = v_from(child(j))
             if (v /= 0) then
                v_to(i) = v;  exit SCAN_CHILDREN
             end if
          end do SCAN_CHILDREN
          if (v_to(i) == 0) then
             vt = vt + 1;  v_to(i) = vt
             v_from(child) = vt
          end if
          deallocate (child)
       end if
    end do
    n_vertices = max (vf, vt)
  end subroutine particle_set_assign_vertices

  subroutine particle_set_to_prt_list (particle_set, prt_list)
    type(particle_set_t), intent(in), target :: particle_set
    type(prt_list_t), intent(out) :: prt_list
    type(particle_t), pointer :: prt
    integer :: i, k
    call prt_list_init (prt_list)
    call prt_list_reset (prt_list, particle_set%n_in + particle_set%n_out)
    k = 0
    do i = 1, particle_set%n_tot
       prt => particle_set%prt(i)
       select case (particle_get_status (prt))
       case (PRT_INCOMING)
          k = k + 1
          call prt_list_set_incoming (prt_list, k, &
               particle_get_pdg (prt), &
               particle_get_momentum (prt), &
               particle_get_p2 (prt))
       case (PRT_OUTGOING)
          k = k + 1
          call prt_list_set_outgoing (prt_list, k, &
               particle_get_pdg (prt), &
               particle_get_momentum (prt), &
               particle_get_p2 (prt))
       end select
    end do
  end subroutine particle_set_to_prt_list

  subroutine particles_test
    use os_interface, only: os_data_t
    type(os_data_t) :: os_data
    type(model_t), pointer :: model
    type(flavor_t), dimension(3) :: flv
    type(color_t), dimension(3) :: col
    type(helicity_t), dimension(3) :: hel
    type(quantum_numbers_t), dimension(3) :: qn
    type(vector4_t), dimension(3) :: p
    type(interaction_t), target :: int1, int2
    type(quantum_numbers_mask_t) :: qn_mask_conn, qn_rest
    type(evaluator_t), target :: eval
    type(interaction_t), pointer :: int
    type(particle_set_t) :: particle_set1, particle_set2
    type(particle_set_t) :: particle_set3, particle_set4
    type(hepmc_event_t) :: hepmc_event
    type(hepmc_iostream_t) :: iostream
    type(prt_list_t) :: prt_list
    integer :: u
    print *, "*** Read model file"
    call syntax_model_file_init ()
    call model_list_read_model &
         (var_str("QCD"), var_str("test.mdl"), os_data, model)
    print *
    print *, "*** Setup production process ***"
    call interaction_init (int1, 2, 0, 1, set_relations=.true.)
    call flavor_init (flv, (/1, -1, 23/), model)
    call helicity_init (hel(3), 1, 1)
    call quantum_numbers_init (qn, flv, hel)
    call interaction_add_state (int1, qn, value=(0.25_default, 0._default))
    call helicity_init (hel(3), 1,-1)
    call quantum_numbers_init (qn, flv, hel)
    call interaction_add_state (int1, qn, value=(0._default, 0.25_default))
    call helicity_init (hel(3),-1, 1)
    call quantum_numbers_init (qn, flv, hel)
    call interaction_add_state (int1, qn, value=(0._default,-0.25_default))
    call helicity_init (hel(3),-1,-1)
    call quantum_numbers_init (qn, flv, hel)
    call interaction_add_state (int1, qn, value=(0.25_default, 0._default))
    call helicity_init (hel(3), 0, 0)
    call quantum_numbers_init (qn, flv, hel)
    call interaction_add_state (int1, qn, value=(0.5_default, 0._default))
    call interaction_freeze (int1)
    p(1) = vector4_moving (45._default, 45._default, 3)
    p(2) = vector4_moving (45._default,-45._default, 3)
    p(3) = p(1) + p(2)
    call interaction_set_momenta (int1, p)
    print *
    print *, "*** Setup decay process ***"
    call interaction_init (int2, 1, 0, 2, set_relations=.true.)
    call flavor_init (flv, (/23, 1, -1/), model)
    call color_init_col_acl (col, (/ 0, 501, 0 /), (/ 0, 0, 501 /))
    call helicity_init (hel, (/ 1, 1, 1/), (/ 1, 1, 1/))
    call quantum_numbers_init (qn, flv, col, hel)
    call interaction_add_state (int2, qn, value=(1._default, 0._default))
    call helicity_init (hel, (/ 1, 1, 1/), (/-1,-1,-1/))
    call quantum_numbers_init (qn, flv, col, hel)
    call interaction_add_state (int2, qn, value=(0._default, 0.1_default))
    call helicity_init (hel, (/-1,-1,-1/), (/ 1, 1, 1/))
    call quantum_numbers_init (qn, flv, col, hel)
    call interaction_add_state (int2, qn, value=(0._default,-0.1_default))
    call helicity_init (hel, (/-1,-1,-1/), (/-1,-1,-1/))
    call quantum_numbers_init (qn, flv, col, hel)
    call interaction_add_state (int2, qn, value=(1._default, 0._default))
    call helicity_init (hel, (/ 0, 1,-1/), (/ 0, 1,-1/))
    call quantum_numbers_init (qn, flv, col, hel)
    call interaction_add_state (int2, qn, value=(4._default, 0._default))
    call helicity_init (hel, (/ 0,-1, 1/), (/ 0, 1,-1/))
    call quantum_numbers_init (qn, flv, col, hel)
    call interaction_add_state (int2, qn, value=(2._default, 0._default))
    call helicity_init (hel, (/ 0, 1,-1/), (/ 0,-1, 1/))
    call quantum_numbers_init (qn, flv, col, hel)
    call interaction_add_state (int2, qn, value=(2._default, 0._default))
    call helicity_init (hel, (/ 0,-1, 1/), (/ 0,-1, 1/))
    call quantum_numbers_init (qn, flv, col, hel)
    call interaction_add_state (int2, qn, value=(4._default, 0._default))
    call flavor_init (flv, (/23, 2, -2/), model)
    call helicity_init (hel, (/ 0, 1,-1/), (/ 0, 1,-1/))
    call quantum_numbers_init (qn, flv, col, hel)
    call interaction_add_state (int2, qn, value=(0.5_default, 0._default))
    call helicity_init (hel, (/ 0,-1, 1/), (/ 0,-1, 1/))
    call quantum_numbers_init (qn, flv, col, hel)
    call interaction_add_state (int2, qn, value=(0.5_default, 0._default))
    call interaction_freeze (int2)
    p(2) = vector4_moving (45._default, 45._default, 2)
    p(3) = vector4_moving (45._default,-45._default, 2)
    call interaction_set_momenta (int2, p)
    call interaction_set_source_link (int2, 1, int1, 3)
    call interaction_write (int1)
    call interaction_write (int2)
    print *
    print *, "*** Concatenate production and decay ***"
    call evaluator_init_product (eval, int1, int2, qn_mask_conn, &
         connections_are_resonant=.true.)
    call evaluator_receive_momenta (eval)
    call evaluator_evaluate (eval)
    call evaluator_write (eval)
    print *
    print *, "*** Factorize as particle list (complete, polarized) ***"
    int => evaluator_get_int_ptr (eval)
    call particle_set_init &
         (particle_set1, int, int, FM_FACTOR_HELICITY, &
          (/0.2_default, 0.2_default/), .false., .true.)
    call particle_set_write (particle_set1)
    print *
    print *, "*** Write this to HEPEUP and print as LHEF format ***"
    call les_houches_events_write_header ()
    call heprup_init ((/2212, 2212/), (/7.e3_default, 7.e3_default/), &
         n_processes=1, unweighted=.true., negative_weights=.false.)
    call heprup_set_process_parameters (1, 1)
    call heprup_write_lhef ()
    call particle_set_fill_hepeup (particle_set1)
    call hepeup_write_lhef ()
    call les_houches_events_write_footer ()
    print *
    print *, "*** Factorize as particle list (in/out only, selected helicity) ***"
    int => evaluator_get_int_ptr (eval)
    call particle_set_init &
         (particle_set2, int, int, FM_SELECT_HELICITY, &
          (/0.9_default, 0.9_default/), .false., .false.)
    call particle_set_write (particle_set2)
    call particle_set_final (particle_set2)
    print *
    print *, "*** Factorize as particle list (complete, selected helicity) ***"
    int => evaluator_get_int_ptr (eval)
    call particle_set_init &
         (particle_set2, int, int, FM_SELECT_HELICITY, &
          (/0.7_default, 0.7_default/), .false., .true.)
    call particle_set_write (particle_set2)
    print *
    print *, "*** Write to HepMC, print, and output to particles_test.hepmc.dat ***"
    call hepmc_event_init (hepmc_event, 11, 127)
    call particle_set_fill_hepmc_event (particle_set2, hepmc_event)
    call hepmc_event_print (hepmc_event)
    call hepmc_iostream_open_out &
         (iostream , var_str ("particles_test.hepmc.dat"))
    call hepmc_iostream_write_event (iostream, hepmc_event)
    call hepmc_iostream_close (iostream)
    print *
    print *, "*** Recover from HepMC file ***"
    call particle_set_final (particle_set2)
    call hepmc_event_final (hepmc_event)
    call hepmc_event_init (hepmc_event)
    call hepmc_iostream_open_in &
         (iostream , var_str ("particles_test.hepmc.dat"))
    call hepmc_iostream_read_event (iostream, hepmc_event)
    call hepmc_iostream_close (iostream)
    call particle_set_init (particle_set2, &
         hepmc_event, model, PRT_DEFINITE_HELICITY)
    call particle_set_write (particle_set2)
    print *
    print *, "*** Factorize (complete, polarized, correlated); write and read again ***"
    int => evaluator_get_int_ptr (eval)
    call particle_set_init &
         (particle_set3, int, int, FM_FACTOR_HELICITY, &
          (/0.7_default, 0.7_default/), .true., .true.)
    call particle_set_write (particle_set3)
    u = free_unit ()
    open (u, action="readwrite", form="unformatted", status="scratch")
    call particle_set_write_raw (particle_set3, u)
    rewind (u)
    call particle_set_read_raw (particle_set4, u)
    close (u)
    print *
    call particle_set_write (particle_set4)
    print *
    print *, "*** Transform to a prt_list object ***"
    call particle_set_to_prt_list (particle_set4, prt_list)
    call prt_list_write (prt_list)
    print *
    print *, "*** Cleanup ***"
    call particle_set_final (particle_set1)
    call particle_set_final (particle_set2)
    call particle_set_final (particle_set3)
    call particle_set_final (particle_set4)
    call evaluator_final (eval)
    call interaction_final (int1)
    call interaction_final (int2)
    call hepmc_event_final (hepmc_event)
  end subroutine particles_test


end module particles