From 7b4d9d268d08df1a07873d794f4675aecfc75a73 Mon Sep 17 00:00:00 2001
From: Paul Romano <paul.k.romano@gmail.com>
Date: Wed, 22 May 2019 06:19:59 -0500
Subject: [PATCH] Change calculation of thermal elastic/inelastic xs

---
 src/thermal.cpp                                      |  4 ++--
 .../asymmetric_lattice/results_true.dat              |  2 +-
 tests/regression_tests/cmfd_feed_2g/results_true.dat | 12 ++++++------
 3 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/src/thermal.cpp b/src/thermal.cpp
index 5db578f9d..40bb19e89 100644
--- a/src/thermal.cpp
+++ b/src/thermal.cpp
@@ -199,7 +199,7 @@ ThermalScattering::calculate_xs(double E, double sqrtkT, int* i_temp,
 
   // Calculate S(a,b) inelastic scattering cross section
   auto& xs = sab.inelastic_sigma_;
-  *inelastic = (1.0 - f) * xs[i_grid] + f * xs[i_grid + 1];
+  *inelastic = xs[i_grid] + f * (xs[i_grid + 1] - xs[i_grid]);
 
   // Check for elastic data
   if (!sab.elastic_e_in_.empty()) {
@@ -231,7 +231,7 @@ ThermalScattering::calculate_xs(double E, double sqrtkT, int* i_temp,
 
       // Calculate S(a,b) elastic scattering cross section
       auto& xs = sab.elastic_P_;
-      *elastic = (1.0 - f) * xs[i_grid] + f * xs[i_grid + 1];
+      *elastic = xs[i_grid] + f*(xs[i_grid + 1] - xs[i_grid]);
     }
   } else {
     // No elastic data
diff --git a/tests/regression_tests/asymmetric_lattice/results_true.dat b/tests/regression_tests/asymmetric_lattice/results_true.dat
index ecc30a056..43f59aa5d 100644
--- a/tests/regression_tests/asymmetric_lattice/results_true.dat
+++ b/tests/regression_tests/asymmetric_lattice/results_true.dat
@@ -1 +1 @@
-4b75e203d06d0fc1b4c4dfcb8c180d6f3df8fa2bc44e9775b59bbfd8f7a3785f956f9a9f301526f69c0f8a963ce2e553e0c62c7f6c696656ce1d47b415af6076
\ No newline at end of file
+4401f503237c94e9d9cfc9f60e0269d5ae5bb67be3225e18c5510ed08616482964e2962a06268751f66a455fac3ddd5faf91555638dfb56fcd09eee60219edff
\ No newline at end of file
diff --git a/tests/regression_tests/cmfd_feed_2g/results_true.dat b/tests/regression_tests/cmfd_feed_2g/results_true.dat
index 8161b2645..4b3dc3c96 100644
--- a/tests/regression_tests/cmfd_feed_2g/results_true.dat
+++ b/tests/regression_tests/cmfd_feed_2g/results_true.dat
@@ -1,5 +1,5 @@
 k-combined:
-1.038883E+00 1.017026E-02
+1.038883E+00 1.017030E-02
 tally 1:
 1.167304E+02
 1.362680E+03
@@ -49,7 +49,7 @@ tally 3:
 0.000000E+00
 2.033842E-02
 4.375294E-05
-4.296338E+00
+4.296339E+00
 9.280716E-01
 3.493776E+00
 6.157094E-01
@@ -74,7 +74,7 @@ tally 3:
 9.717439E+01
 4.724254E+02
 8.435691E-01
-3.666151E-02
+3.666152E-02
 6.192881E+01
 1.924016E+02
 0.000000E+00
@@ -82,7 +82,7 @@ tally 3:
 1.796382E-02
 3.190854E-05
 4.343238E+00
-9.514039E-01
+9.514040E-01
 3.504683E+00
 6.157615E-01
 0.000000E+00
@@ -106,7 +106,7 @@ tally 3:
 9.885292E+01
 4.888720E+02
 9.509199E-01
-4.670951E-02
+4.670952E-02
 tally 4:
 0.000000E+00
 0.000000E+00
@@ -383,7 +383,7 @@ cmfd balance
 1.08402E-03
 1.09178E-03
 5.45977E-04
-4.45554E-04
+4.45555E-04
 4.01147E-04
 3.71025E-04
 3.57715E-04