From 54feb3fe20a86edd18fc2436e4fdbaa7222925fc Mon Sep 17 00:00:00 2001
From: Paul Romano <romano7@gmail.com>
Date: Mon, 26 Mar 2012 19:51:37 -0400
Subject: [PATCH] Another fix for mesh tracklength tallies.

---
 src/physics.F90 |  6 +++---
 src/tally.F90   | 13 +++++++++----
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/src/physics.F90 b/src/physics.F90
index 03ca45354d..ca9d389ec1 100644
--- a/src/physics.F90
+++ b/src/physics.F90
@@ -81,9 +81,6 @@ contains
        ! Select smaller of the two distances
        distance = min(d_boundary, d_collision)
 
-       ! Save coordinates for tallying purposes
-       p % last_xyz = p % coord0 % xyz
-
        ! Advance particle
        coord => p % coord0
        do while (associated(coord))
@@ -131,6 +128,9 @@ contains
           p % surface = NONE
           call collision()
 
+          ! Save coordinates for tallying purposes
+          p % last_xyz = p % coord0 % xyz
+
           ! Set last material to none since cross sections will need to be
           ! re-evaluated
           p % last_material = NONE
diff --git a/src/tally.F90 b/src/tally.F90
index cb701e7070..5d304e4ddb 100644
--- a/src/tally.F90
+++ b/src/tally.F90
@@ -552,7 +552,7 @@ contains
        ! since multiple bins can be scored to with a single track
        
        if (t % n_filter_bins(FILTER_MESH) > 0) then
-          call score_tl_on_mesh(tracklength_tallies(i))
+          call score_tl_on_mesh(tracklength_tallies(i), distance)
           cycle
        end if
 
@@ -621,9 +621,10 @@ contains
 ! these tallies, it is possible to score to multiple mesh cells for each track.
 !===============================================================================
 
-  subroutine score_tl_on_mesh(index_tally)
+  subroutine score_tl_on_mesh(index_tally, d_track)
 
     integer, intent(in) :: index_tally
+    real(8), intent(in) :: d_track
 
     integer :: i                    ! loop index for filter/score bins
     integer :: j                    ! loop index for direction
@@ -657,8 +658,8 @@ contains
     ! CHECK IF THIS TRACK INTERSECTS THE MESH
 
     ! Copy starting and ending location of particle
-    xyz0 = p % last_xyz
-    xyz1 = p % coord0 % xyz
+    xyz0 = p % coord0 % xyz - (d_track - TINY_BIT) * p % coord0 % uvw
+    xyz1 = p % coord0 % xyz  - TINY_BIT * p % coord0 % uvw
 
     ! Determine indices for starting and ending location
     m => meshes(t % mesh)
@@ -671,6 +672,10 @@ contains
        if (.not. mesh_intersects(m, xyz0, xyz1)) return
     end if
 
+    ! Reset starting and ending location
+    xyz0 = p % coord0 % xyz - d_track * p % coord0 % uvw
+    xyz1 = p % coord0 % xyz
+
     ! =========================================================================
     ! CHECK FOR SCORING COMBINATION FOR FILTERS OTHER THAN MESH