message: Used HostReadWrite as suggested.
diff: @@ -493,8 +493,8 @@ void ParGridFunction::GetDerivative(int comp, int der_comp,
  gcomm.Bcast(overlap);
  // Accumulate for all dofs.
  - gcomm.Reduce<double>(der.GetMemory(), GroupCommunicator::Sum);
  - gcomm.Bcast<double>(der.GetMemory());
  + gcomm.Reduce<double>(der.HostReadWrite(), GroupCommunicator::Sum);
  + gcomm.Bcast<double>(der.HostReadWrite());
  for (int i = 0; i < overlap.Size(); i++)
  {
  