MPI Tutorial, by Blaise Barney, §9. Collective Communication
RS/6000 SP: Practical MPI Programming, IBM Red Book.
The relevant parts for this lecture is Chapter 2 §2.3. Though somewhat dated, this is an excellent source of information about MPI. Note that the code examples are written in Fortran.
$(PUB)/lib/PPF, with examples in $(PUB)/examples/PPF (See the README file for important information about using the software).