From 8e6b61711644effe17af82d58ddb196e748be798 Mon Sep 17 00:00:00 2001
From: Brody Bassett <brbass@umich.edu>
Date: Fri, 15 Dec 2017 02:19:50 -0500
Subject: [PATCH] Added a check for minimum energy in the source sampling. Set
 multigroup min and max energies and removed check for these after samping the
 source.

---
 src/input_xml.F90     |  5 +++++
 src/source.F90        | 12 +++---------
 src/source_header.F90 | 11 +++++++----
 3 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/src/input_xml.F90 b/src/input_xml.F90
index 1eb1a0aee6..72aaa6b7b7 100644
--- a/src/input_xml.F90
+++ b/src/input_xml.F90
@@ -4215,11 +4215,16 @@ contains
     rev_energy_bins = energy_bins
     energy_bins = energy_bins(num_energy_groups + 1:1:-1)
 
+    ! Get the midpoint of the energy groups
     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))
     end do
 
+    ! Get the minimum and maximum energies
+    energy_min_neutron = energy_bins(num_energy_groups + 1)
+    energy_max_neutron = energy_bins(1)
+    
     ! Get the datasets present in the library
     call get_groups(file_id, names)
     n_libraries = size(names)
diff --git a/src/source.F90 b/src/source.F90
index 5a58a6a855..557120e979 100644
--- a/src/source.F90
+++ b/src/source.F90
@@ -129,15 +129,9 @@ contains
 
     ! If running in MG, convert site % E to group
     if (.not. run_CE) 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(rev_energy_bins, num_energy_groups + 1, &
-             site % E), 8)
-        site % E = num_energy_groups + 1 - site % E
-      end if
+      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
 
     ! Set the random number generator back to the tracking stream.
diff --git a/src/source_header.F90 b/src/source_header.F90
index a60696996a..fca05d8167 100644
--- a/src/source_header.F90
+++ b/src/source_header.F90
@@ -9,7 +9,7 @@ module source_header
   use error
   use geometry, only: find_cell
   use material_header, only: materials
-  use nuclide_header, only: energy_max_neutron
+  use nuclide_header, only: energy_min_neutron, energy_max_neutron
   use particle_header, only: Particle
   use string, only: to_lower
   use xml_interface
@@ -275,9 +275,12 @@ contains
     ! Check for monoenergetic source above maximum neutron energy
     select type (energy => this % energy)
     type is (Discrete)
-      if (any(energy % x >= energy_max_neutron)) then
+      if (any(energy % x > energy_max_neutron)) then
         call fatal_error("Source energy above range of energies of at least &
              &one cross section table")
+      else if (any(energy % x < energy_min_neutron)) then
+        call fatal_error("Source energy below range of energies of at least &
+             &one cross section table")
       end if
     end select
 
@@ -285,8 +288,8 @@ contains
       ! Sample energy spectrum
       site % E = this % energy % sample()
 
-      ! resample if energy is greater than maximum neutron energy
-      if (site % E < energy_max_neutron) exit
+      ! Resample if energy falls outside minimum or maximum neutron energy
+      if (site % E < energy_max_neutron .and. site % E > energy_min_neutron) exit
     end do
 
     ! Set delayed group