!........................................................................
!
! Subroutine :
!
! Description:  propogate twiss to center of quad
!
! Arguments  :          
!
! Mod/Commons:    
!
! Calls      :      
!
! Author     : 
!
! Modified   :     
!             
!........................................................................
!
!
! $Log$
! Revision 1.8  2007/03/21 16:02:21  dcs
! a%eta_lab -> x%eta, etc.
!
! Revision 1.7  2007/01/30 16:15:14  dcs
! merged with branch_bmad_1.
!
! Revision 1.4  2003/11/18 00:58:22  dcs
! volt to voltage
!
! Revision 1.3  2003/09/23 18:31:29  dlr
! with carriage return, uses lattice in constraint file
!
! Revision 1.2  2003/04/30 17:14:53  cesrulib
! dlr's changes since last import
!
! Revision 1.1.1.1  2002/12/13 19:23:29  cesrulib
! import bmadz
!
!
!........................................................................
!
subroutine quad_twiss ( lat, quad)

  use bmad
  use bmadz_mod


  use zquad_lens_mod
  implicit none

  type (lat_struct)  lat
  type (ele_struct)  ele0, ele1, ele2
  type (zquad_struct) quad

  integer i, j
  real(rp) b_ave

  call identify_quads (lat, quad)

  do j = 1, quad%n   !get average beta and maximum beta in quads
    i=quad%lens(j)%ix
    if(lat%ele(i)%key == sbend$ .or. lat%ele(i)%key == rbend$)then
      quad%lens(j)%a%beta_ave = b_ave(lat%ele(i)%a%beta,-lat%ele(i)%a%alpha, lat%ele(i)%value(k1$), lat%ele(i)%value(l$)) 
      quad%lens(j)%b%beta_ave = b_ave(lat%ele(i)%b%beta,-lat%ele(i)%b%alpha, -lat%ele(i)%value(k1$), lat%ele(i)%value(l$)) 
     else
      call quad_beta_ave (lat%ele(i), quad%lens(j)%a%beta_ave, quad%lens(j)%b%beta_ave)
    endif
!  propogate twiss to center of quad

    ele1 = lat%ele(i)
    if(ele1%mat6_calc_method /= taylor$)then
     ele1%value(k1$) = lat%ele(i)%value(k1$)
     ele1%value(l$) = 0.5 * lat%ele(i)%value(l$)
     call set_flags_for_changed_attribute(ele1, .true.)
     call make_mat6(ele1, lat%param)
     call twiss_propagate1 ( lat%ele(i-1), ele1)
    else
     ele1 = lat%ele(i)
    endif

    ele0 = lat%ele(i-1)   ! Twiss at the start of the quad
    ele2 = lat%ele(i)     ! Twiss at the end   of the quad

    quad%lens(j)%a%beta_max = max(ele0%a%beta, ele1%a%beta, ele2%a%beta)
    quad%lens(j)%b%beta_max = max(ele0%b%beta, ele1%b%beta, ele2%b%beta)

    quad%lens(j)%x%eta_max = max(ele0%x%eta, ele1%x%eta, ele2%x%eta)
    quad%lens(j)%y%eta_max = max(ele0%y%eta, ele1%y%eta, ele2%y%eta)

    quad%lens(j)%a%eta_max = max(ele0%a%eta, ele1%a%eta, ele2%a%eta)
    quad%lens(j)%b%eta_max = max(ele0%b%eta, ele1%b%eta, ele2%b%eta)

  end do

  return
  end