From fe8cbcc487849d4e3cbd6e445cdf534f04faaf29 Mon Sep 17 00:00:00 2001
From: Adam G Nelson <nelsonag@umich.edu>
Date: Tue, 12 Nov 2019 05:07:43 -0600
Subject: [PATCH] Updated Mgxs::calculate_xs interface to use the particle,
 matching interface for continuous energy equivalent

---
 include/openmc/mgxs.h | 11 +++--------
 src/mgxs.cpp          | 15 +++++++--------
 src/particle.cpp      | 10 +++++-----
 3 files changed, 15 insertions(+), 21 deletions(-)

diff --git a/include/openmc/mgxs.h b/include/openmc/mgxs.h
index 71e8c7ec9..3dfd6ba4c 100644
--- a/include/openmc/mgxs.h
+++ b/include/openmc/mgxs.h
@@ -11,6 +11,7 @@
 
 #include "openmc/constants.h"
 #include "openmc/hdf5_interface.h"
+#include "openmc/particle.h"
 #include "openmc/xsdata.h"
 
 
@@ -167,15 +168,9 @@ class Mgxs {
 
     //! \brief Calculates cross section quantities needed for tracking.
     //!
-    //! @param gin Incoming energy group.
-    //! @param sqrtkT Temperature of the material.
-    //! @param u Incoming particle direction.
-    //! @param total_xs Resultant total cross section.
-    //! @param abs_xs Resultant absorption cross section.
-    //! @param nu_fiss_xs Resultant nu-fission cross section.
+    //! @param p The particle whose attributes set which MGXS to get.
     void
-    calculate_xs(int gin, double sqrtkT, Direction u,
-         double& total_xs, double& abs_xs, double& nu_fiss_xs);
+    calculate_xs(Particle& p);
 
     //! \brief Sets the temperature index in cache given a temperature
     //!
diff --git a/src/mgxs.cpp b/src/mgxs.cpp
index 53e24c67c..0dd8c73cc 100644
--- a/src/mgxs.cpp
+++ b/src/mgxs.cpp
@@ -600,8 +600,7 @@ Mgxs::sample_scatter(int gin, int& gout, double& mu, double& wgt)
 //==============================================================================
 
 void
-Mgxs::calculate_xs(int gin, double sqrtkT, Direction u,
-     double& total_xs, double& abs_xs, double& nu_fiss_xs)
+Mgxs::calculate_xs(Particle& p)
 {
   // Set our indices
 #ifdef _OPENMP
@@ -609,13 +608,13 @@ Mgxs::calculate_xs(int gin, double sqrtkT, Direction u,
 #else
   int tid = 0;
 #endif
-  set_temperature_index(sqrtkT);
-  set_angle_index(u);
+  set_temperature_index(p.sqrtkT_);
+  set_angle_index(p.u_local());
   XsData* xs_t = &xs[cache[tid].t];
-  total_xs = xs_t->total(cache[tid].a, gin);
-  abs_xs = xs_t->absorption(cache[tid].a, gin);
-
-  nu_fiss_xs = fissionable ? xs_t->nu_fission(cache[tid].a, gin) : 0.;
+  p.macro_xs_.total = xs_t->total(cache[tid].a, p.g_);
+  p.macro_xs_.absorption = xs_t->absorption(cache[tid].a, p.g_);
+  p.macro_xs_.nu_fission =
+    fissionable ? xs_t->nu_fission(cache[tid].a, p.g_) : 0.;
 }
 
 //==============================================================================
diff --git a/src/particle.cpp b/src/particle.cpp
index da93c6723..b430d3a06 100644
--- a/src/particle.cpp
+++ b/src/particle.cpp
@@ -202,12 +202,12 @@ Particle::transport()
           model::materials[material_]->calculate_xs(*this);
         }
       } else {
-        // Get the MG data
-        data::mg.macro_xs_[material_].calculate_xs(g_, sqrtkT_,
-          this->u_local(), macro_xs_.total, macro_xs_.absorption,
-          macro_xs_.nu_fission);
+        // Get the MG data; unlike the CE case above, we have to re-calculate
+        // cross sections for every collision since the cross sections may
+        // be angle-dependent
+        data::mg.macro_xs_[material_].calculate_xs(*this);
 
-        // Finally, update the particle group since we know we are multi-group
+        // Update the particle's group while we know we are multi-group
         g_last_ = g_;
       }
     } else {