just a couple of minor comments to chapter 4 ( collective communication). I apologize if some of the issues have already been brought up. a) page 128, line 35: "MPI_Bcast broadcasts a message from the process with rank root to all processes of the group, itself included." I would suggest to modify the last part of the sentence to :"..., itself included for intracommunicators" (or something similar), since the statement does not make sense for inter-communicators, and we do not distinguish at that point in the text the two types of communicators yet. b) a similar issues arises for gather (page 130, line 1). E.g. the sentence could be re-structured slightly to :"If comm is an intracommunicator, each process....". The same issue for Gatherv (page 131, line 40). c) I would suggest to extend the descriptions of the examples in section 4.6.1 to explicitly mentioning, that comm is an intracomm in those examples. Similarly for the examples in section 4.7.1; section 4.8.1; example 4.15 and 4.16 on page 154 d) In the examples 4.17, 4.18 and 4.19 on pages 157--159, the code executes MPI_Comm_rank on MPI_COMM_WORLD, but the subsequent MPI_Reduce ( and the if myrank==root section) on 'comm'. This should probably be the same communicator, else the code doesn't make sense. I suggest to replace MPI_COMM_WORLD with comm, following the procedure of the previous examples in that section; alternatively, we could add a line with comm=MPI_COMM_WORLD, in order to get around the problem mentioned in bullet c). Thanks Edgar -- Edgar Gabriel Assistant Professor Parallel Software Technologies Lab http://pstl.cs.uh.edu Department of Computer Science University of Houston Philip G. Hoffman Hall, Room 524 Houston, TX-77204, USA Tel: +1 (713) 743-3857 Fax: +1 (713) 743-3335