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2004 is my twelfth year of working on this book and much of it comes from earlier work and the experience of four previous books. In this book, as in my previous books, I owe a great deal to the many students at the Stanford Exploration Project. I would like to mention some with particularly notable contributions (in approximate historical order).

The concept of this book began along with the PhD thesis of Jeff Thorson. Before that, we imagers thought of our field as "an hoc collection of good ideas" instead of as "adjoints of forward problems". Bill Harlan understood most of the preconditioning issues long before I did. All of us have a longstanding debt to Rick Ottolini who built a cube movie program long before anyone else in the industry had such a blessing.

My first book was built with a typewriter and ancient technologies. In early days each illustration would be prepared without reusing packaged code. In assembling my second book I found I needed to develop common threads and code them only once and make this code systematic and if not idiot proof, then ``idiot resistant''. My early attempts to introduce ``seplib'' were not widely welcomed until Stew Levin rebuilt everything making it much more robust. My second book was typed in the troff text language. I am indebted to Kamal Al-Yahya who not only converted that book to LATEX, but who wrote a general-purpose conversion program that became used internationally.

Early days were a total chaos of plot languages. I and all the others at SEP are deeply indebted to Joe Dellinger who starting from work of Dave Hale, produced our internal plot language ``vplot'' which gave us reproducibiliy and continuity over decades. Now, for example, our plots seamlessly may be directed to postscript (and PDF), Xwindow, or the web. My second book required that illustrations be literally taped onto the sheet containing the words. All of us benefitted immensely from the work of Steve Cole who converted Joe's vplot language to postscript which was automatically integrated with the text.

When I began my third book I was adapting liberally from earlier work. I began to realize the importance of being able to reproduce any earlier calculation and began building rules and file-naming conventions for ``reproducible research''. This would have been impossible were it not for Dave Nichols who introduced cake, a variant of the UNIX software building program make. Martin Karrenbach continued the construction of our invention of ``reproducible research'' and extended it to producing reproducible research reports on CD-ROM, an idea well ahead of its time. Some projects were fantastic for their time but had the misfortune of not being widely adopted, ultimately becoming unsupportable. In this catagory was Dave and Martin's implementation xtex, a magnificent way of embedding reproducible research in an electronic textbook. When cake suffered the same fate as xtex, Matthias Schwab saved us from mainstream isolation by bringing our build procedures into the popular GNU world.

Coming to the present textbook I mention Bob Clapp. He made numerous contributions. When Fortran77 was replaced by Fortran90, he rewrote Ratfor. For many years I (and many of us) depended on Ratfor as our interface to Fortran and as a way of presenting uncluttered code. Bob rewrote Ratfor from scratch merging it with other SEP-specific software tools (Sat) making Ratfor90. Bob prepared the interval-velocity examples in this book. Bob also developed most of the ``geostat'' ideas and examples in this book. Morgan Brown introduced the texture examples that we find so charming. Paul Sava totally revised the book's presentation of least-squares solvers making them more palatable to students and making more honest our claim that in each case the results you see were produced by the code you see.

One name needs to be singled out. Sergey Fomel converted all the examples in this book from my original Fortran 77 to a much needed modern style of Fortran 90. After I discovered the helix idea and its wide-ranging utility, he adapted all the relevant examples in this book to use it. If you read Fomel's programs, you can learn effective application of that 1990's revolution in coding style known as ``object orientation.''

This electronic book, ``Geophysical Exploration by Example,'' is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This book is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Massachusetts Ave., Cambridge, MA 02139, USA.

©Jon Claerbout  
April 27, 2004

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