message: Fix global error computation for the ZZ error estimator in parallel.
diff: #include "../mesh/nurbs.hpp"
  #include "../general/text.hpp"
  +#ifdef MFEM_USE_MPI
  +#include "pfespace.hpp"
  +#endif
  +
  #include <limits>
  #include <cstring>
  #include <string>
  #include <iostream>
  #include <algorithm>
  +
  namespace mfem
  {
  @@ -3652,7 +3657,15 @@ double ZZErrorEstimator(BilinearFormIntegrator &blfi,
  }
  }
  }
  -
  +#ifdef MFEM_USE_MPI
  + auto pfes = dynamic_cast<ParFiniteElementSpace*>(ufes);
  + if (pfes)
  + {
  + auto process_local_error = total_error;
  + MPI_Allreduce(&process_local_error, &total_error, 1, MPI_DOUBLE,
  + MPI_SUM, pfes->GetComm());
  + }
  +#endif // MFEM_USE_MPI
  return std::sqrt(total_error);
  }
  