Hello. Please note the instruction at line 105 (the *MPI_Alltoall* call) and the comment on the line 108. You only need to run the program once. The program takes 3 arguments from the command line: 1-How many numbers does each processor produce locally 2-The range bounds of numbers to produces randomly(like , say, 2 to 20, entered as 2 20) so to run, e.g, type mpirun -n 4 ./a.out 4 0 15 Note that the number of processors should be a power of 2 I personally think that maybe the reason for this bug is that the *index*and the *size* of each dimension are ignored and that only the *base address* and the *displacement* is assumed. I read in Intel developer's manual that you need 4 parameters to access an element of a multi-dimensional array. I wonder if you can apply this.