subroutine qp_read_twiss_data (unit, err_flag, z, bx, by, eta) ! read in the data.

  use bmad

  implicit none

    real(rp), allocatable :: bx(:), by(:), z(:), eta(:), ax(:), ay(:), etap(:)
    integer n, ios, unit, n_tot
    logical err_flag
!    character*16, allocatable :: ele_name(:)
    character*100 string
   n=0
   do while(.true.)
    read(unit,'(a100)', IOSTAT=ios)string
    if(ios == -1) exit
    n=n+1
!    if(ios /= 0)print *, ' Error reading fort.22'
   end do

   print *, 'n points = ', n

!  n=n+1
  if(.not. allocated(bx))then
   allocate(bx(1:n), by(1:n), ax(1:n), ay(1:n), z(1:n), eta(1:n), etap(1:n))
   print *, 'allocate' 
!  allocate (ele_name(1:n))
  endif
 n_tot = n
 print *,' rewind '
 rewind(unit)

   do n=1,n_tot
    read(unit,'(16x,7es12.4)', IOSTAT=ios) z(n), bx(n), &
                   by(n), ax(n), ay(n), &
                   eta(n),  etap(n)
    if(ios == -1) exit
!    if(ios /=0)print *, ' Error reading fort.22'
   end do
 
 rewind(unit) 
 print *,' rewind again'
  end subroutine