Lösungsvorschlag

#include <cassert>
#include <cstdio>
#include <mpi.h>
#include <hpc/matvec/gematrix.h>
#include <hpc/mpi/matrix.h>
#include <hpc/mpi/vector.h>
#include <hpc/matvec/apply.h>

int main(int argc, char** argv) {
   MPI_Init(&argc, &argv);

   int nof_processes; MPI_Comm_size(MPI_COMM_WORLD, &nof_processes);
   int rank; MPI_Comm_rank(MPI_COMM_WORLD, &rank);
   assert(nof_processes == 2);

   using namespace hpc::matvec;
   using namespace hpc::mpi;
   using namespace hpc::aux;

   unsigned int nof_rows = 3;
   unsigned int nof_cols = 7;

   if (rank == 0) {
      GeMatrix<double> A(nof_rows, nof_cols, StorageOrder::RowMajor);
      using Index = GeMatrix<double>::Index;
      apply(A, [](double& val, Index i, Index j) -> void {
         val = i * 100 + j;
      });
      auto row = A.row(2);
      auto col = A.col(0);
      MPI_Datatype row_type = get_type(row);
      MPI_Datatype col_type = get_type(col);

      MPI_Send(&row(0), 1, row_type, 1, 0, MPI_COMM_WORLD);
      MPI_Send(&col(0), 1, col_type, 1, 0, MPI_COMM_WORLD);

      /* receive it back for verification */
      DenseVector<double> vec1(nof_cols), vec2(nof_rows);
      MPI_Datatype vec1_type = get_type(vec1);
      MPI_Datatype vec2_type = get_type(vec2);
      MPI_Status status;
      MPI_Recv(&vec1(0), 1, vec1_type, 1, 0, MPI_COMM_WORLD, &status);
      MPI_Recv(&vec2(0), 1, vec2_type, 1, 0, MPI_COMM_WORLD, &status);

      /* verify it */
      apply(vec1, [=](double& val, Index i) {
         if (val != row(i)) {
            printf("verification failed for row(%d): %lg vs %lg\n",
               (int)i, val, row(i));
         }
      });
      apply(vec2, [=](double& val, Index i) {
         if (val != col(i)) {
            printf("verification failed for col(%d): %lg vs %lg\n",
               (int)i, val, col(i));
         }
      });
   } else {
      DenseVector<double> vec1(nof_cols), vec2(nof_rows);
      MPI_Datatype vec1_type = get_type(vec1);
      MPI_Datatype vec2_type = get_type(vec2);
      MPI_Status status;
      MPI_Recv(&vec1(0), 1, vec1_type, 0, 0, MPI_COMM_WORLD, &status);
      MPI_Recv(&vec2(0), 1, vec2_type, 0, 0, MPI_COMM_WORLD, &status);

      /* send it back for verification */
      MPI_Send(&vec1(0), 1, vec1_type, 0, 0, MPI_COMM_WORLD);
      MPI_Send(&vec2(0), 1, vec2_type, 0, 0, MPI_COMM_WORLD);
   }
   MPI_Finalize();
}

#ifndef HPC_MPI_VECTOR_H
#define HPC_MPI_VECTOR_H 1

#include <mpi.h>
#include <hpc/matvec/densevector.h>
#include <hpc/matvec/isdensevector.h>
#include <hpc/mpi/fundamental.h>

namespace hpc { namespace mpi {

template<typename Vector>
typename std::enable_if<hpc::matvec::IsDenseVector<Vector>::value,
   MPI_Datatype>::type
get_type(const Vector& vector) {
   using ElementType = typename Vector::ElementType;
   MPI_Datatype datatype;
   MPI_Type_vector(
      /* count = */ vector.length,
      /* blocklength = */ 1,
      /* stride = */ vector.inc,
      /* element type = */ get_type(vector(0)),
      /* newly created type = */ &datatype);
   MPI_Type_commit(&datatype);
   return datatype;
}

} } // namespaces mpi, hpc

#endif // HPC_MPI_VECTOR_H