subroutine get_quad_locs(lat, zquad, xquad)  !zquad is the position, and xquad is positive or negative 1
  use bmad
  implicit none
  type(lat_struct) lat
  real(rp), allocatable :: zquad(:), xquad(:)
  integer i,n
  n=0
!print *,' lat%n_ele_track =', lat%n_ele_track
  do i=1, lat%n_ele_track
!   print '(i10,a16,1x,es12.4)',i,lat%ele(i)%name, lat%ele(i)%s
   if(lat%ele(i)%key == quadrupole$)n=n+1
  end do

  allocate(zquad(1:n), xquad(1:n))
 n=0
  do i=1,lat%n_ele_track
   if(lat%ele(i)%key == quadrupole$)then
     n=n+1
      zquad(n) = lat%ele(i)%s - 0.5 * lat%ele(i)%value(l$)
      xquad(n) = sign(lat%ele(i)%value(l$), lat%ele(i)%value(k1$))
   endif
 end do
!do i=1,n
! print '(2es12.4)',zquad(i), xquad(i)
!end do
 return
 end subroutine