From 960f71e276c753ec056978b182cff751728f81cc Mon Sep 17 00:00:00 2001
From: Adam G Nelson <nelsonag@umich.edu>
Date: Mon, 8 Oct 2018 14:01:52 -0400
Subject: [PATCH] whoops, including files

---
 include/openmc/physics_mg.h | 20 ++++++++++++++++++++
 src/physics_mg.cpp          | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100644 include/openmc/physics_mg.h
 create mode 100644 src/physics_mg.cpp

diff --git a/include/openmc/physics_mg.h b/include/openmc/physics_mg.h
new file mode 100644
index 0000000000..e570de917a
--- /dev/null
+++ b/include/openmc/physics_mg.h
@@ -0,0 +1,20 @@
+//! \file physics_mg.h
+//! Methods needed to perform the collision physics for multi-group mode
+
+#ifndef OPENMC_PHYSICS_MG_H
+#define OPENMC_PHYSICS_MG_H
+
+#include "openmc/particle.h"
+
+namespace openmc {
+
+//==============================================================================
+// SCATTER
+//==============================================================================
+
+//! \brief Samples the scattering event
+extern "C" void
+scatter(Particle* p, const double* energy_bin_avg);
+
+} // namespace openmc
+#endif // OPENMC_PHYSICS_MG_H
diff --git a/src/physics_mg.cpp b/src/physics_mg.cpp
new file mode 100644
index 0000000000..27379a2d6c
--- /dev/null
+++ b/src/physics_mg.cpp
@@ -0,0 +1,32 @@
+#include "openmc/physics_mg.h"
+
+#include "openmc/constants.h"
+#include "openmc/math_functions.h"
+#include "openmc/mgxs_interface.h"
+
+namespace openmc {
+
+void scatter(Particle* p, const double* energy_bin_avg)
+{
+  // Adjust indices for Fortran to C++ indexing
+  // TODO: Remove when no longer needed
+  int gin = p->last_g - 1;
+  int gout = p->g - 1;
+  int i_mat = p->material - 1;
+  macro_xs[i_mat].sample_scatter(gin, gout, p->mu, p->wgt);
+
+  // Adjust return value for fortran indexing
+  // TODO: Remove when no longer needed
+  p->g = gout + 1;
+
+  // Rotate the angle
+  rotate_angle_c(p->coord[0].uvw, p->mu, nullptr);
+
+  // Update energy value for downstream compatability (in tallying)
+  p->E = energy_bin_avg[gout];
+
+  // Set event component
+  p->event = EVENT_SCATTER;
+}
+
+} //namespace openmc