Rewrite communicateGroupRates() to do a single sum().

opm/simulators/wells/WellStateFullyImplicitBlackoil.hpp

@@ -1007,29 +1007,73 @@ namespace Opm
         }
 
         template<class Comm>
-        void communicateGroupRates(const Comm& comm) {
-            // sum over all nodes
-            for (auto& x : injection_group_rein_rates) {
-                comm.sum(x.second.data(), x.second.size());
+        void communicateGroupRates(const Comm& comm)
+        {
+            // Note that injection_group_vrep_rates is handled separate from
+            // the forAllGroupData() function, since it contains single doubles,
+            // not vectors.
+
+            // Create a function that calls some function
+            // for all the individual data items to simplify
+            // the further code.
+            auto forAllGroupData = [&](auto& func) {
+                for (auto& x : injection_group_rein_rates) {
+                    func(x.second);
+                }
+                for (auto& x : production_group_reduction_rates) {
+                    func(x.second);
+                }
+                for (auto& x : injection_group_reduction_rates) {
+                    func(x.second);
+                }
+                for (auto& x : injection_group_reservoir_rates) {
+                    func(x.second);
+                }
+                for (auto& x : production_group_rates) {
+                    func(x.second);
+                }
+                for (auto& x : well_rates) {
+                    func(x.second);
+                }
+            };
+
+            // Compute the size of the data.
+            std::size_t sz = 0;
+            auto computeSize = [&sz](const auto& v) {
+                sz += v.size();
+            };
+            forAllGroupData(computeSize);
+            sz += injection_group_vrep_rates.size();
+
+            // Make a vector and collect all data into it.
+            std::vector<double> data(sz);
+            std::size_t pos = 0;
+            auto collect = [&data, &pos](const auto& v) {
+                for (const auto& x : v) {
+                    data[pos++] = x;
+                }
+            };
+            forAllGroupData(collect);
+            for (const auto& x : injection_group_vrep_rates) {
+                data[pos++] = x.second;
             }
+            assert(pos == sz);
+
+            // Communicate it with a single sum() call.
+            comm.sum(data.data(), data.size());
+
+            // Distribute the summed vector to the data items.
+            pos = 0;
+            auto distribute = [&data, &pos](auto& v) {
+                for (auto& x : v) {
+                    x = data[pos++];
+                }
+            };
+            forAllGroupData(distribute);
             for (auto& x : injection_group_vrep_rates) {
-                x.second = comm.sum(x.second);
-            }
-            for (auto& x : production_group_reduction_rates) {
-                comm.sum(x.second.data(), x.second.size());
-            }
-            for (auto& x : injection_group_reduction_rates) {
-                comm.sum(x.second.data(), x.second.size());
-            }
-            for (auto& x : injection_group_reservoir_rates) {
-                comm.sum(x.second.data(), x.second.size());
-            }
-            for (auto& x : production_group_rates) {
-                comm.sum(x.second.data(), x.second.size());
-            }
-            for (auto& x : well_rates) {
-                comm.sum(x.second.data(), x.second.size());
+                x.second = data[pos++];
             }
+            assert(pos == sz);
         }
 
         template<class Comm>