!........................................................................
!
! Subroutine : TRANSFER_LINE_MATRIX_CALC
!                 (lat,start_name,end_name, mat, detmn_dag)
!
! Description: Compute energy dependence of each term of 4X4 matrix from 
!              and including  START_NAME to END_NAME
!
! Arguments  : 
!    Input:
!       LAT  -- lat_struct: Lat
!
!    Output:
!       mat   -- transfer matrix from start_name to end_name
!       detmn_dag -- determinant of m + adjoint n, m=mat(3:2,4:2), 
!                    n=mat(1:2,3:4)         
!
! Mod/Commons: use bmad   
!
! Calls      :      
!
! Author     : 
!
! Modified   :     
!             
!........................................................................
!
!
! $Log$
! Revision 1.6  2007/01/30 16:15:14  dcs
! merged with branch_bmad_1.
!
! Revision 1.3  2003/12/05 15:23:42  dcs
! Fix standard nonconforming stuff.
!
! Revision 1.2  2003/04/30 17:14:56  cesrulib
! dlr's changes since last import
!
! Revision 1.1.1.1  2002/12/13 19:23:30  cesrulib
! import bmadz
!
!
!........................................................................
!


subroutine transfer_line_matrix_calc(lat, start_name, end_name, mat, detmn_dag)

  use bmad


  implicit none

  type (lat_struct)  lat

  real(rp) mat(6,6)
  real(rp) mn_dag(2,2), detmn_dag

  integer i,  n
  integer ixs, ixe, ix

  logical started, ended
  character*12 start_name, end_name

  ixs = index(start_name, ' ') - 1
  ixe = index(end_name, ' ') - 1

  call mat_make_unit (mat)       ! form unit matrix
  n=0
  started = .false.
  ended = .false.
  do while (.not. ended)
  n = n+1
    i = n
    if(n > lat%n_ele_track ) i = n - lat%n_ele_track
    if(lat%ele(i)%name(1:ixs) == start_name(1:ixs) )started = .true.
    if(started .and. lat%ele(i)%name(1:ixe) == end_name(1:ixe) ) &
         ended = .true.
    if(started) &
         mat(1:6,1:6) = matmul (lat%ele(i)%mat6(1:6,1:6), mat(1:6,1:6))
  enddo

  mn_dag(1,1) = mat(3,1) + mat(2,4)
  mn_dag(1,2) = mat(3,2) - mat(1,4)
  mn_dag(2,1) = mat(4,1) - mat(2,3)
  mn_dag(2,2) = mat(4,2) + mat(1,3)
  detmn_dag = mn_dag(1,1) * mn_dag(2,2) - mn_dag(1,2) * mn_dag(2,1)

end subroutine