[Mpi-21] review of chapter 4

Edgar Gabriel gabriel at [hidden]
Fri Mar 7 17:18:09 CST 2008

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).


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

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