Parallel Environment for AIX 5L V4.1
Hitchhiker's Guide

What is all this?

In The Hitchhiker's Guide to the Galaxy, a novel by Douglas Adams, there are many situations and states that are similar to those experienced by a person who is becoming familiar with PE. That is why we fashioned the book after Mr. Adams's... the parallels were obvious. We decided to included these references to make reading this book a little more pleasant. We hope you enjoy it. If not, please let us know by submitting the Reader's Comment form at the back of this manual, or by sending us comments electronically (see the Edition Notice on page ii for directions on how to do this). Since The Hitchhiker's Guide to the Galaxy material in this book is not technical in nature, we will not open customer-reported APARs (Authorized Program Analysis Reports) related to it.

The chapter titles in this book are taken directly from references within The Hitchhiker's Guide to the Galaxy. For those unfamiliar with Mr. Adams' work, or if our references are less than obvious, the objective of each chapter is described below.

• Hitching a lift on the Vogon constructor ship familiarizes you with the Parallel Operating Environment (POE). The Hitchhiker's Guide to the Galaxy begins with Arthur Dent, earthman and main character, being suddenly swept aboard an alien space ship; the Vogon Constructor Ship. Once on board the ship, Arthur is completely bewildered -- the way you must feel right now if you are completely new to the IBM Parallel Environment for AIX and do not have any idea where to start.
• The answer is 42 covers parallelization techniques and discusses their advantages and disadvantages. The Hitchhiker's Guide to the Galaxy tells us that the galaxy's biggest supercomputer was asked to come up with an answer to the ultimate question of Life, the Universe, and Everything. The answer was 42. The problem is that once the characters in the book have the answer, they realize they do not know what the question is. We have used this title for the chapter that discusses how you take a working serial program (you know the answer is the serial algorithm) and create a parallel program that gives the same answer (you need to determine what the parallel constructs are to implement the algorithm).
• Don't panic outlines the possible causes for a parallel application to fail to execute correctly, and how the tools available with the IBM Parallel Environment for AIX can be used to identify and correct problems. What do you do when your parallel program does not work right, and how many different ways are there for it not to work right? As The Hitchhiker's Guide to the Galaxy advises us, Don't Panic.
• So long and thanks for all the fish discusses some of the ways you can optimize the performance of your parallel program. In The Hitchhiker's Guide to the Galaxy, we learn that dolphins are the most intelligent life form on Earth. Their departing message to mankind as they leave the Earth is So long and thanks for all the fish. We are not leaving earth, but we will leave you with some parting hints on tuning the performance of your program.
• Babel fish helps you understand how to translate your MPL parallel program into a program that conforms to the MPI standard. In The Hitchhiker's Guide to the Galaxy the Babel Fish is a tiny fish that, when inserted into your ear, can make any language understandable to you. It would be nice if we could give you a Babel Fish to migrate your Message Passing Library (MPL) applications to Message Passing Interface (MPI), but unfortunately, they are not available here in the unfashionable end of the western spiral arm of the galaxy (the nearest supplier is in Alpha Centauri).
• Mostly harmless provides you with some general guidelines for creating safe parallel MPI programs.
• Appendix A, A sample program to illustrate messages provides a sample program, run with the maximum level of error messages. It points out the various types of messages you can expect, and tells you what they mean.
• Appendix B, Parallel Environment internals provides some additional information about how the IBM Parallel Environment for AIX (PE) work, with respect to your application.

The purpose of this book is to get you started creating parallel programs with PE. Once you have mastered these initial concepts, you will need to know more about how PE works. For information on the Parallel Operating Environment (POE), see IBM Parallel Environment for AIX: Operation and Use, Volume 1 For information on PE tools, see IBM Parallel Environment for AIX: Operation and Use, Volume 2.