Fix element geometry at mirror center.

bmad/code/twiss_and_track_intra_ele.f90

@@ -98,6 +98,22 @@ recursive subroutine twiss_and_track_intra_ele (ele, param, l_start, l_end, trac
   return
 endif
 
+! mirror, multilayer_mirror, and crystal are exceptional if floor coords needed
+
+if (ele%key == mirror$ .or. ele%key == multilayer_mirror$ .or. ele%key == crystal$) then
+  do_downstream = (track_downstream_end .or. (orbit_start%location == downstream_end$ .and. orbit_start%ix_ele == ele%ix_ele))
+  if (.not. do_downstream) then  ! Then must be center
+    if (present(orbit_end)) orbit_end = orbit_start   ! Note: Orbit does not make sense here.
+    if (present(ele_end)) then
+      ele_end = ele
+      if (logic_option(.false., compute_floor_coords)) call ele_geometry (ele_start%floor, ele, ele_end%floor, 0.5_rp)
+    endif
+    return
+  endif
+endif
+
+
+
 ! zero length element:
 ! Must ignore track_upstream_end and track_downstream_end since they do not make sense in this case.
 

bmad/geometry/ele_geometry.f90

@@ -286,17 +286,16 @@ recursive subroutine ele_geometry (floor_start, ele, floor_end, len_scale, ignor
 
 !---------------------------
 ! General case where layout is not in the horizontal plane
-! Note: 
 
 has_multipole_rot_tilt = .false.
 if (key == multipole$) then
   call multipole_ele_to_kt (ele, .true., ix_pole_max, knl, tilt)
   if (knl(0) /= 0 .and. tilt(0) /= 0) has_multipole_rot_tilt = .true.
 endif
 
-if (((key == mirror$  .or. key == sbend$ .or. key == rf_bend$ .or. key == multilayer_mirror$) .and. &
-         ele%value(ref_tilt_tot$) /= 0) .or. phi /= 0 .or. psi /= 0 .or. key == patch$ .or. &
-         key == crystal$ .or. has_multipole_rot_tilt) then
+if (phi /= 0 .or. psi /= 0 .or. key == patch$ .or. key == crystal$ .or. has_multipole_rot_tilt .or. &
+     ((key == sbend$ .or. key == rf_bend$) .and. ele%value(ref_tilt_tot$) /= 0) .or. &
+     ((key == mirror$  .or.  key == multilayer_mirror$) .and. (ele%value(ref_tilt_tot$) /= 0 .or. abs(len_factor - 0.5) < 0.25))) then
 
   select case (key)
 
@@ -371,6 +370,7 @@ recursive subroutine ele_geometry (floor_start, ele, floor_end, len_scale, ignor
     call floor_angles_to_w_mat (theta, phi, psi, w_mat)
     floor%r = floor0%r + matmul(w_mat, r_vec)
 
+    ! The factor of pi/2 rotates to surface coordinates.
     if (len_factor == 0.5_rp) then
       if (ele%key == crystal$) then
         s_mat = w_mat_for_bend_angle(angle-pi/2, ele%value(ref_tilt_tot$) + ele%value(tilt_corr$), r_vec)