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Difference Equations to Differential Equations: An Introduction to Calculus

AuthorDan Sloughter Entered2004-01-18 21:16:08 by Ryanov
Editedit data record FreedomCopylefted, but with restrictions on modification and/or sale (disclaimer)
SubjectQ.A - Mathematics. Computer science (analysis)
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a roundabout approach
by Ben Crowell (crowell09 at (change 09 to current year)) on 2004-03-03 16:52:56, review #389
This book is distributed as a collection of 54 Adobe Acrobat files. It's licensed under the GPL copyleft license. That warms my heart as an open-source enthusiast, but it's slightly strange, for a couple of reasons. First, the GPL is a software license, and is less suitable as a copyleft license for books than the GFDL or a CC license. Also, the source code of the book isn't available (it appears to have been done in LaTeX), which I think makes it legally impossible under the GPL to redistribute the book, whereas the author's intent in GPL-ing it was presumably to make it freely distributable.

The book is well written, and seems to have been well designed for practical classroom use. The approach is visual and intuitive, and there are lots and lots of graphs and numerical calculations. I felt, however, that it took a long time to get going, and the idiosyncratic selection of topics might make it difficult to use at many schools. Although the very first page gives a nice clear explanation of what calculus is about, we then have to wait until about page 136 to learn any calculus. I say "about" because of the inconvenient way in which the book is split up into many separate files, each of which has page numbers starting from 1. I had to estimate page number 136 by weighing part of the book on a postal scale. Related to this problem is the fact that the book has no index or table of contents.

The book uses many numerical examples, which gives it a modern feeling . After all, calculus was invented by Newton and Leibniz because they needed to do calculations in closed form, but nowadays it's more natural to solve many problems on a computer, using a spreadsheet or a programming language. The book has a problem, however, in integrating the computer stuff with the didactic parts and the homework problems. No indication is given of how the numerical examples were actually computed. The author may consider it a trivial task to set up a spreadsheet or write a ten-line program in Python or Mathematica, but it's not so trivial for many students, and they will need extensive guidance from elsewhere to be able to carry out such computations for themselves. This makes the text incomplete in practical terms: any instructor wanting to use it would have to come up with extensive support materials to go with it. It also contributes to my sense that the book lacks focus. Students have a hard enough time learning the basic concepts and techniques of integration and differentiation, but to use this book, they would also have to learn about computer programming and difference equations. Adding to the bloat is the author's tendency to discuss every possible pathological case before moving on to the main event. It's a little like a parent trying to explain sex to his child, but feeling obliged to explain foot fetishes before getting on with where babies come from.

The examples that students are expected to do numerically also presuppose quite a bit of resourcefulness and insight. For instance, one of the homework problems asks the student to sum the series 4(1-1/3+1/5-1/7+...) numerically, adding up "...a sufficient number of terms to enable you to guess the value of the sum," which turns out to be pi. The trouble is that over 600 terms are required to get the sum to settle down in the second decimal place, which is about the minimum I'd want to see to convince me it was pi. Pity the poor student who first tries 10 terms on a calculator, then 50 terms on a spreadsheet, and then finally realizes he's going to need to write a Python program to get the job done. Of course, some students might enjoy the process, but my experience (teaching college science majors taking introductory physics) is that the majority don't consider computers to be fun.

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