From fae2888b26b04258dbb8b3ba812c9c6bf7736147 Mon Sep 17 00:00:00 2001
From: Brody Bassett <brbass@umich.edu>
Date: Mon, 11 Dec 2017 04:10:32 -0500
Subject: [PATCH] Fixed issue in source.F90 with fixing energy bins.

---
 src/input_xml.F90                   |  5 +++++
 src/mgxs_header.F90                 |  5 ++++-
 src/source.F90                      | 11 ++++++-----
 src/tallies/tally_filter_energy.F90 |  4 ++--
 4 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/src/input_xml.F90 b/src/input_xml.F90
index b7bc88e25d..1eb1a0aee6 100644
--- a/src/input_xml.F90
+++ b/src/input_xml.F90
@@ -4201,6 +4201,7 @@ contains
       num_delayed_groups = 0
     end if
 
+    allocate(rev_energy_bins(num_energy_groups + 1))
     allocate(energy_bins(num_energy_groups + 1))
 
     if (attribute_exists(file_id, "group structure")) then
@@ -4210,6 +4211,10 @@ contains
       call fatal_error("'group structure' attribute must exist!")
     end if
 
+    ! First reverse the order of energy_groups
+    rev_energy_bins = energy_bins
+    energy_bins = energy_bins(num_energy_groups + 1:1:-1)
+
     allocate(energy_bin_avg(num_energy_groups))
     do i = 1, num_energy_groups
       energy_bin_avg(i) = HALF * (energy_bins(i) + energy_bins(i + 1))
diff --git a/src/mgxs_header.F90 b/src/mgxs_header.F90
index b282397245..46ad181d32 100644
--- a/src/mgxs_header.F90
+++ b/src/mgxs_header.F90
@@ -221,12 +221,15 @@ module mgxs_header
   ! Number of delayed groups
   integer :: num_delayed_groups
 
-  ! Energy group structure
+  ! Energy group structure with decreasing energy
   real(8), allocatable :: energy_bins(:)
 
   ! Midpoint of the energy group structure
   real(8), allocatable :: energy_bin_avg(:)
 
+  ! Energy group structure with increasing energy
+  real(8), allocatable :: rev_energy_bins(:)
+  
 contains
 
 !===============================================================================
diff --git a/src/source.F90 b/src/source.F90
index 0689cb4035..5a58a6a855 100644
--- a/src/source.F90
+++ b/src/source.F90
@@ -15,7 +15,7 @@ module source
   use hdf5_interface,   only: file_create, file_open, file_close, read_dataset
   use math
   use message_passing,  only: rank
-  use mgxs_header,      only: energy_bins, num_energy_groups
+  use mgxs_header,      only: rev_energy_bins, num_energy_groups
   use output,           only: write_message
   use particle_header,  only: Particle
   use random_lcg,       only: prn, set_particle_seed, prn_set_stream
@@ -129,13 +129,14 @@ contains
 
     ! If running in MG, convert site % E to group
     if (.not. run_CE) then
-      if (site % E <= energy_bins(1)) then
-        site % E = real(1, 8)
-      else if (site % E > energy_bins(num_energy_groups + 1)) then
+      if (site % E <= rev_energy_bins(1)) then
         site % E = real(num_energy_groups, 8)
+      else if (site % E > rev_energy_bins(num_energy_groups + 1)) then
+        site % E = real(1, 8)
       else
-        site % E = real(binary_search(energy_bins, num_energy_groups + 1, &
+        site % E = real(binary_search(rev_energy_bins, num_energy_groups + 1, &
              site % E), 8)
+        site % E = num_energy_groups + 1 - site % E
       end if
     end if
 
diff --git a/src/tallies/tally_filter_energy.F90 b/src/tallies/tally_filter_energy.F90
index b2498d4b5a..2a247cf358 100644
--- a/src/tallies/tally_filter_energy.F90
+++ b/src/tallies/tally_filter_energy.F90
@@ -8,7 +8,7 @@ module tally_filter_energy
   use constants
   use error
   use hdf5_interface
-  use mgxs_header,         only: num_energy_groups, energy_bins
+  use mgxs_header,         only: num_energy_groups, rev_energy_bins
   use particle_header,     only: Particle
   use settings,            only: run_CE
   use string,              only: to_str
@@ -75,7 +75,7 @@ contains
     ! ordering of the library and tallying systems).
     if (.not. run_CE) then
       if (n == num_energy_groups + 1) then
-        if (all(this % bins == energy_bins)) &
+        if (all(this % bins == rev_energy_bins)) &
              then
           this % matches_transport_groups = .true.
         end if