Add mode flip warning in Tao. (#806)

bmad/code/twiss_propagate_all.f90

@@ -1,9 +1,10 @@
 !+
-! Subroutine twiss_propagate_all (lat, ix_branch, err_flag, ie_start, ie_end, zero_uncalculated)
+! Subroutine twiss_propagate_all (lat, ix_branch, err_flag, ie_start, ie_end)
 !
 ! Subroutine to propagate the twiss, coupling, and dispersion parameters from 
 ! the start to the end of a lattice branch.
 !
+! If there is a problem, Twiss parameters not calculated in range [ie_start, ie_end] are set to zero.
 !
 ! Input:
 !   lat                -- lat_struct: lattice.
@@ -12,15 +13,13 @@
 !   ie_start           -- integer, optional: Starting element index. Default is 0.
 !                           Note: The first element at which the Twiss parameters are calculated is ie_start+1.
 !   ie_end             -- integer, optional: Ending element index, Default is branch%n_ele_track.
-!   zero_uncalculated  -- logical, optional: Set to zero Twiss parameters not calculated in 
-!                           range [ie_start, ie_end]? Default is True.
 !
 ! Output:
 !   lat          -- lat_struct: Lattice with parameters computed for the branch.
 !   err_flag     -- logical, optional: Set True if there is an error. False otherwise.
 !-
 
-subroutine twiss_propagate_all (lat, ix_branch, err_flag, ie_start, ie_end, zero_uncalculated)
+subroutine twiss_propagate_all (lat, ix_branch, err_flag, ie_start, ie_end)
 
 use bmad_interface, except_dummy => twiss_propagate_all
 
@@ -35,7 +34,7 @@ subroutine twiss_propagate_all (lat, ix_branch, err_flag, ie_start, ie_end, zero
 integer n, n_track, i_start, i_end
 integer, optional :: ix_branch, ie_start, ie_end
 
-logical, optional :: err_flag, zero_uncalculated
+logical, optional :: err_flag
 logical err
 
 character(*), parameter :: r_name = 'twiss_propagate_all'
@@ -81,21 +80,19 @@ subroutine twiss_propagate_all (lat, ix_branch, err_flag, ie_start, ie_end, zero
   if (err) return
 enddo
 
-if (logic_option(.true., zero_uncalculated)) then
-  do n = 0, i_start-1
-    branch%ele(n)%a = twiss_struct()
-    branch%ele(n)%b = twiss_struct()
-    branch%ele(n)%x = xy_disp_struct()
-    branch%ele(n)%y = xy_disp_struct()
-  enddo
-
-  do n = i_end+1, n_track
-    branch%ele(n)%a = twiss_struct()
-    branch%ele(n)%b = twiss_struct()
-    branch%ele(n)%x = xy_disp_struct()
-    branch%ele(n)%y = xy_disp_struct()
-  enddo
-endif
+do n = 0, i_start-1
+  branch%ele(n)%a = twiss_struct()
+  branch%ele(n)%b = twiss_struct()
+  branch%ele(n)%x = xy_disp_struct()
+  branch%ele(n)%y = xy_disp_struct()
+enddo
+
+do n = i_end+1, n_track
+  branch%ele(n)%a = twiss_struct()
+  branch%ele(n)%b = twiss_struct()
+  branch%ele(n)%x = xy_disp_struct()
+  branch%ele(n)%y = xy_disp_struct()
+enddo
 
 ! Make sure final mode is same as initial mode
 

bmad/modules/bmad_routine_interface.f90

@@ -3089,12 +3089,12 @@ subroutine twiss_propagate1 (ele1, ele2, err)
   logical, optional :: err
 end subroutine
 
-subroutine twiss_propagate_all (lat, ix_branch, err_flag, ie_start, ie_end, zero_uncalculated)
+subroutine twiss_propagate_all (lat, ix_branch, err_flag, ie_start, ie_end)
   import
   implicit none
   type (lat_struct), target :: lat
   integer, optional :: ix_branch, ie_start, ie_end
-  logical, optional :: err_flag, zero_uncalculated
+  logical, optional :: err_flag
 end subroutine
 
 subroutine twiss_to_1_turn_mat (twiss, phi, mat2)

tao/code/tao_lattice_calc_mod.f90

@@ -52,7 +52,7 @@ subroutine tao_single_track (tao_lat, calc_ok, ix_branch, print_err)
 character(*), parameter :: r_name = "tao_single_track"
 
 logical, optional :: print_err
-logical calc_ok, err, radiation_fluctuations_on
+logical calc_ok, err, radiation_fluctuations_on, mode_flip
 
 !
 
@@ -161,7 +161,6 @@ subroutine tao_single_track (tao_lat, calc_ok, ix_branch, print_err)
   endif
 
   bmad_com%radiation_fluctuations_on = radiation_fluctuations_on
-
 endif
 
 ! Twiss
@@ -188,6 +187,13 @@ subroutine tao_single_track (tao_lat, calc_ok, ix_branch, print_err)
       call twiss_propagate_all (lat, ix_branch, err, 0, ix_lost - 1)
     endif
 
+    mode_flip = any(branch%ele(1:branch%n_ele_track)%mode_flip)
+    if (mode_flip .and. .not. tao_branch%mode_flip_here) then
+      call out_io(s_warn$, r_name, '*Mode flip* detected! Care must be used in interpreting Twiss parameter!', &
+                                   'See the Bmad manual on linear optics for more information.')
+    endif
+    tao_branch%mode_flip_here = mode_flip
+
   else
     branch%param%stable = .false.
     branch%param%unstable_factor = 0  ! Unknown

tao/code/tao_struct.f90

@@ -938,6 +938,7 @@ module tao_struct
   logical has_open_match_element
   logical :: plot_cache_valid = .false.                       ! Valid plotting data cache?
   logical :: spin_map_valid = .false.
+  logical :: mode_flip_here = .false.                         ! Twiss parameter mode flip seen?
 end type
 
 ! Structure to hold a single lat_struct (model, base, or design) in