From b2c064cc357415b4699302dabf7e0ea6d1f40d9d Mon Sep 17 00:00:00 2001
From: Patrick Shriwise <pshriwise@gmail.com>
Date: Tue, 8 Oct 2019 11:34:26 -0500
Subject: [PATCH] Updates for MPI runs.

---
 src/volume_calc.cpp | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/src/volume_calc.cpp b/src/volume_calc.cpp
index 23bb08f822..13cfcf569e 100644
--- a/src/volume_calc.cpp
+++ b/src/volume_calc.cpp
@@ -325,11 +325,30 @@ std::vector<VolumeCalculation::Result> VolumeCalculation::execute() const
       }
     }
 
+#ifdef OPENMC_MPI
+    // update maximum error value on all processes
+    if (mpi::master) {
+      for (int i = 1; i < mpi::n_procs; i++) {
+        MPI_Send(&max_vol_err, 1, MPI_DOUBLE, i, 0, mpi::intracomm);
+      }
+    } else {
+      MPI_Recv(&max_vol_err, 1, MPI_DOUBLE, 0, 0, mpi::intracomm, MPI_STATUS_IGNORE);
+    } 
+#endif
+    
     // return results of the calculation
     if (trigger_type_ == ThresholdType::NONE || max_vol_err < threshold_) { 
       return results;
     }    
 
+#ifdef OPENMC_MPI
+    // if iterating in MPI, need to zero indices and hits to they aren't counted twice
+    if (!mpi::master) {
+      for (auto& v : master_indices) { std::fill(v.begin(), v.end(), 0.0); }
+      for (auto& v : master_hits) { std::fill(v.begin(), v.end(), 0.0); }
+    }
+#endif
+
   } // end while
 }