Fix unnecessary allreduce

diff --git a/include/deal.II/lac/solver_gmres.h b/include/deal.II/lac/solver_gmres.h
index 6df1e9a0ec9120a62ba04b9426ee681ce934bcb9..baa9a04b14ca540486c8901e54989a8b2ca09af5 100644 (file)
--- a/include/deal.II/lac/solver_gmres.h
+++ b/include/deal.II/lac/solver_gmres.h
@@ -1283,8 +1283,12 @@ namespace internal
             }
         }
 
-      return std::sqrt(
-        Utilities::MPI::sum(norm_vv_temp, block(vv, 0).get_mpi_communicator()));
+      if (delayed_reorthogonalization)
+        return std::numeric_limits<double>::signaling_NaN();
+      else
+        return std::sqrt(
+          Utilities::MPI::sum(norm_vv_temp,
+                              block(vv, 0).get_mpi_communicator()));
     }