Revised MG code so that the energy group indices are 0-based instead of 1-based. Next commit will perform some code cleanup enabled by this change.

src/mgxs_interface.cpp

@@ -298,12 +298,12 @@ get_nuclide_xs(int index, int xstype, int gin, const int* gout,
   int gout_c;
   const int* gout_c_p;
   if (gout != nullptr) {
-    gout_c = *gout - 1;
+    gout_c = *gout;
     gout_c_p = &gout_c;
   } else {
     gout_c_p = gout;
   }
-  return data::mg.nuclides_[index].get_xs(xstype, gin - 1, gout_c_p, mu, dg);
+  return data::mg.nuclides_[index].get_xs(xstype, gin, gout_c_p, mu, dg);
 }
 
 //==============================================================================
@@ -315,12 +315,12 @@ get_macro_xs(int index, int xstype, int gin, const int* gout,
   int gout_c;
   const int* gout_c_p;
   if (gout != nullptr) {
-    gout_c = *gout - 1;
+    gout_c = *gout;
     gout_c_p = &gout_c;
   } else {
     gout_c_p = gout;
   }
-  return data::mg.macro_xs_[index].get_xs(xstype, gin - 1, gout_c_p, mu, dg);
+  return data::mg.macro_xs_[index].get_xs(xstype, gin, gout_c_p, mu, dg);
 }
 
 } // namespace openmc

src/particle.cpp

@@ -123,7 +123,7 @@ Particle::from_source(const Bank* src)
   } else {
     g_ = static_cast<int>(src->E);
     g_last_ = static_cast<int>(src->E);
-    E_ = data::mg.energy_bin_avg_[g_ - 1];
+    E_ = data::mg.energy_bin_avg_[g_];
   }
   E_last_ = E_;
 }
@@ -203,7 +203,7 @@ Particle::transport()
         }
       } else {
         // Get the MG data
-        data::mg.macro_xs_[material_].calculate_xs(g_ - 1, sqrtkT_,
+        data::mg.macro_xs_[material_].calculate_xs(g_, sqrtkT_,
           this->u_local(), macro_xs_.total, macro_xs_.absorption,
           macro_xs_.nu_fission);
 

src/particle_restart.cpp

@@ -52,7 +52,7 @@ void read_particle_restart(Particle& p, int& previous_run_mode)
   // Set energy group and average energy in multi-group mode
   if (!settings::run_CE) {
     p.g_ = p.E_;
-    p.E_ = data::mg.energy_bin_avg_[p.g_ - 1];
+    p.E_ = data::mg.energy_bin_avg_[p.g_];
   }
 
   // Set particle last attributes

src/physics_mg.cpp

@@ -77,22 +77,14 @@ sample_reaction(Particle* p)
 void
 scatter(Particle* p)
 {
-  // Adjust indices for Fortran to C++ indexing
-  // TODO: Remove when no longer needed
-  int gin = p->g_last_ - 1;
-  int gout = p->g_ - 1;
-  int i_mat = p->material_;
-  data::mg.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;
+  data::mg.macro_xs_[p->material_].sample_scatter(p->g_last_, p->g_, p->mu_,
+                                                  p->wgt_);
 
   // Rotate the angle
   p->u() = rotate_angle(p->u(), p->mu_, nullptr);
 
   // Update energy value for downstream compatability (in tallying)
-  p->E_ = data::mg.energy_bin_avg_[gout];
+  p->E_ = data::mg.energy_bin_avg_[p->g_];
 
   // Set event component
   p->event_ = EVENT_SCATTER;
@@ -148,8 +140,8 @@ create_fission_sites(Particle* p, std::vector<Particle::Bank>& bank)
     // the energy in the fission bank
     int dg;
     int gout;
-    data::mg.macro_xs_[p->material_].sample_fission_energy(p->g_ - 1, dg, gout);
-    site.E = gout + 1;
+    data::mg.macro_xs_[p->material_].sample_fission_energy(p->g_, dg, gout);
+    site.E = gout;
     site.delayed_group = dg + 1;
 
     // Set the delayed group on the particle as well

src/source.cpp

@@ -309,11 +309,11 @@ Particle::Bank sample_external_source()
   // Sample source site from i-th source distribution
   Particle::Bank site {model::external_sources[i].sample()};
 
-  // If running in MG, convert site % E to group
+  // If running in MG, convert site.E to group
   if (!settings::run_CE) {
     site.E = lower_bound_index(data::mg.rev_energy_bins_.begin(),
       data::mg.rev_energy_bins_.end(), site.E);
-    site.E = data::mg.num_energy_groups_ - site.E;
+    site.E = data::mg.num_energy_groups_ - site.E - 1.;
   }
 
   // Set the random number generator back to the tracking stream.

src/tallies/filter_energy.cpp

@@ -61,9 +61,9 @@ const
 {
   if (p->g_ != F90_NONE && matches_transport_groups_) {
     if (estimator == ESTIMATOR_TRACKLENGTH) {
-      match.bins_.push_back(data::mg.num_energy_groups_ - p->g_);
+      match.bins_.push_back(data::mg.num_energy_groups_ - p->g_ - 1);
     } else {
-      match.bins_.push_back(data::mg.num_energy_groups_ - p->g_last_);
+      match.bins_.push_back(data::mg.num_energy_groups_ - p->g_last_ - 1);
     }
     match.weights_.push_back(1.0);
 
@@ -104,7 +104,7 @@ EnergyoutFilter::get_all_bins(const Particle* p, int estimator,
                               FilterMatch& match) const
 {
   if (p->g_ != F90_NONE && matches_transport_groups_) {
-    match.bins_.push_back(data::mg.num_energy_groups_ - p->g_);
+    match.bins_.push_back(data::mg.num_energy_groups_ - p->g_ - 1);
     match.weights_.push_back(1.0);
 
   } else {

src/tallies/tally_scoring.cpp

@@ -348,9 +348,9 @@ score_fission_eout(const Particle* p, int i_tally, int i_score, int score_bin)
       // determine outgoing energy group from fission bank
       auto g_out = static_cast<int>(bank.E);
 
-      // modify the value so that g_out = 1 corresponds to the highest energy
+      // modify the value so that g_out = 0 corresponds to the highest energy
       // bin
-      g_out = eo_filt.n_bins() - g_out;
+      g_out = eo_filt.n_bins() - g_out - 1;
 
       // change outgoing energy bin
       simulation::filter_matches[i_eout_filt].bins_[i_bin] = g_out;