! Module file: twin_operators
!
! CNS module
! **********
!
! Authors: Axel Brunger and Paul Adams
!
! copyright Yale University
!
! Function:
!    Return the twinning operator for a specified point group
!
! Requirements:
!    None

module {twin_operators}

(
  &point_group;
  &operator_num;
  &twin_oper;
)

set message ? end
evaluate ($message_old=$result)
set echo ? end
evaluate ($echo_old=$result)
if ( $log_level = verbose ) then
  set echo=on message=normal end
else
  set echo=off message=off end
end if

checkversion 1.3

evaluate (&twin_oper="VOID")

if     ( &point_group = 3 ) then
  if     ( &operator_num = 1 ) then
    evaluate (&twin_oper="h,-h-k,-l")
  elseif ( &operator_num = 2 ) then
    evaluate (&twin_oper="h+k,-k,-l")
  elseif ( &operator_num = 3 ) then
    evaluate (&twin_oper="-h,-k,l")
  end if
elseif ( &point_group = 4 ) then
  if     ( &operator_num = 1 ) then
    evaluate (&twin_oper="h,-k,-l")
  end if
elseif ( &point_group = 6 ) then
  if     ( &operator_num = 1 ) then
    evaluate (&twin_oper="h,-h-k,-l")
  end if
elseif ( &point_group = 321 ) then
  if     ( &operator_num = 1 ) then
    evaluate (&twin_oper="-h,-k,l")
  end if
elseif ( &point_group = 312 ) then
  if     ( &operator_num = 1 ) then
    evaluate (&twin_oper="-h,-k,l")
  end if
elseif ( &point_group = 23 ) then
  if     ( &operator_num = 1 ) then
    evaluate (&twin_oper="k,-h,l")
  end if
end if

set message=$message_old echo=$echo_old end