## It may be tempting to pass the same argument to both operand and result on the root process
eg
```cpp
/* Illegal call */
MPI_Reduce(&sum, &sum, 1, MPI_INT, MPI_SUM, 0, MPI_COMM_WORLD);
```

This is called **aliasing** of arguments and it is illegal to alias out or in/out arguments in any MPI function