================
Lösungsvorschlag
================

---- CODE (type=cpp) ----------------------------------------------------------
template<typename MA, typename MB>
typename std::enable_if<
   hpc::matvec::IsGeMatrix<MA>::value && hpc::matvec::IsGeMatrix<MB>::value &&
      std::is_same<typename MA::ElementType, typename MB::ElementType>::value,
   int>::type
scatter_by_row(const MA& A, MB& B, int root, MPI_Comm comm) {
   assert(A.numCols == B.numCols);

   int nof_processes; MPI_Comm_size(comm, &nof_processes);
   int rank; MPI_Comm_rank(comm, &rank);

   hpc::aux::Slices<int> slices(nof_processes, A.numRows);
   std::vector<int> counts(nof_processes);
   std::vector<int> offsets(nof_processes);

   MPI_Datatype rowtype_A = get_row_type(A);
   for (int i = 0; i < nof_processes; ++i) {
      if (i < A.numRows) {
         counts[i] = slices.size(i);
         offsets[i] = slices.offset(i);
      } else {
         counts[i] = 0; offsets[i] = 0;
      }
   }
   int recvcount = counts[rank];
   assert(B.numRows == recvcount);

   MPI_Datatype rowtype_B = get_row_type(B);

   /* OpenMPI implementation of Debian wheezy expects void* instead
      of const void*; hence we need to remove const */
   return MPI_Scatterv((void*) &A(0, 0), &counts[0], &offsets[0], rowtype_A,
      &B(0, 0), recvcount, rowtype_B, root, comm);
}

template<typename MA, typename MB>
typename std::enable_if<
   hpc::matvec::IsGeMatrix<MA>::value && hpc::matvec::IsGeMatrix<MB>::value &&
      std::is_same<typename MA::ElementType, typename MB::ElementType>::value,
   int>::type
gather_by_row(const MA& A, MB& B, int root, MPI_Comm comm) {
   assert(A.numCols == B.numCols);

   int nof_processes; MPI_Comm_size(comm, &nof_processes);
   int rank; MPI_Comm_rank(comm, &rank);

   hpc::aux::Slices<int> slices(nof_processes, B.numRows);
   std::vector<int> counts(nof_processes);
   std::vector<int> offsets(nof_processes);

   for (int i = 0; i < nof_processes; ++i) {
      if (i < B.numRows) {
         counts[i] = slices.size(i);
         offsets[i] = slices.offset(i);
      } else {
         counts[i] = 0; offsets[i] = 0;
      }
   }
   int sendcount = counts[rank];
   assert(A.numRows == sendcount);

   MPI_Datatype rowtype_A = get_row_type(A);
   MPI_Datatype rowtype_B = get_row_type(B);

   /* OpenMPI implementation of Debian wheezy expects void* instead
      of const void*; hence we need to remove const */
   return MPI_Gatherv((void*) &A(0, 0), sendcount, rowtype_A,
      &B(0, 0), &counts[0], &offsets[0], rowtype_B, root, comm);
}
-------------------------------------------------------------------------------

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