What do these two functions do?

Question

C++ / C#

The task was to find the closest neighboring elements of the vector

int getMinDifferenceOneProc(const std::vector <int> Vec) {
  int difMin = INT_MAX;
  if (Vec.size() != 0) {
    for (int i = 0; i < static_cast<int>(Vec.size()) - 1; i++) {
      if (difMin > abs(Vec[i] - Vec[i + 1]))
        difMin = abs(Vec[i] - Vec[i + 1]);
    }
  }
  if (Vec.size() == 1) {
    return 0;
  }
  return difMin;
}

int getMinDifference(const std::vector <int> Vec) {
  int difMin = INT_MAX;
  int size, rank;
  MPI_Comm_size(MPI_COMM_WORLD, &size);
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  MPI_Status status;

  int modSize = Vec.size() - 1;
  int modf = modSize / size;
  int res = modSize % size;

  if (rank == 0) {
    if (modf > 0) {
      for (int noProc = 1; noProc < size; noProc++)
        MPI_Send(&Vec[res] + modf * noProc, modf + 1, MPI_INT, noProc, 0, MPI_COMM_WORLD);
    }
  } else {
    if (modf > 0) {
      std::vector<int> tmp(modf + 1);
      MPI_Recv(&tmp[0], modf + 1, MPI_INT, 0, MPI_ANY_TAG, MPI_COMM_WORLD, &status);
      int minD = getMinDifferenceOneProc(tmp);
      MPI_Send(&minD, 1, MPI_INT, 0, 0, MPI_COMM_WORLD);
    }
  }
  if (rank == 0) {
    int procRest;
    std::vector<int> tmp(Vec.begin(), Vec.begin() + 1 + modf + res);
    difMin = getMinDifferenceOneProc(tmp);
    if (modf > 0) {
      for (int noProc = 1; noProc < size; noProc++) {
        MPI_Recv(&procRest, 1, MPI_INT, noProc, 0, MPI_COMM_WORLD, &status);
        difMin = std::min(difMin, procRest);
      }
    }
  }
  return difMin;
}

Answer 1

What do these two functions do?

And what is the difficulty in taking and reading their code in order to understand what they are doing?
Help on MPI functions can be found e.g. here .