MPI_Gather and MPI_Scatter

 

   0: send =  1 2 3 4
   1: send =  5 6 7 8
   2: send =  9 10 11 12
   3: send =  13 14 15 16
   0: recv =  1 5 9 13
   1: recv =  2 6 10 14
   2: recv =  3 7 11 15
   3: recv =  4 8 12 16