message: fix the left-right/up-down direction in code to make communication correct
diff: @@ -64,22 +64,22 @@ Settings::Settings(int argc, char *argv[], int rank, int nproc) : rank{rank}
  // determine neighbors
  if (posx == 0)
  - rank_left = -1;
  + rank_up = -1;
  else
  - rank_left = rank - 1;
  + rank_up = rank - 1;
  if (posx == npx - 1)
  - rank_right = -1;
  + rank_down = -1;
  else
  - rank_right = rank + 1;
  + rank_down = rank + 1;
  if (posy == 0)
  - rank_up = -1;
  + rank_left = -1;
  else
  - rank_up = rank - npx;
  + rank_left = rank - npx;
  if (posy == npy - 1)
  - rank_down = -1;
  + rank_right = -1;
  else
  - rank_down = rank + npx;
  + rank_right = rank + npx;
  }
  