MPI_Comm_rank(comm, &rank);
int* sbuf = (int *) xbt_malloc(size * size * sizeof(int));
int* rbuf = (int *) xbt_malloc(size * size * sizeof(int));
MPI_Comm_rank(comm, &rank);
int* sbuf = (int *) xbt_malloc(size * size * sizeof(int));
int* rbuf = (int *) xbt_malloc(size * size * sizeof(int));