Street Fighting Mathematics

Sanjay Mahajan’s Street Fighting Mathematics is a short, dense, and engaging book that explores some mathematical problem-solving techniques not typically taught in math class.

These techniques, favored by engineers and scientists who are usually more interested in the answer to a question than in the mathematical theory that gets them there, can turn seemingly intractable problems into simple ones, often just by a change in perspective.

For example, the book offers a short treatment of Feynman’s differentiating-under-the-integral approach, one of the more famous “back of the napkin” techniques.  Mahajan even “guesses” the definite integral that yields the area under the bell curve, using dimensional analysis the likes of which I’ve never seen.

A “Street Fighting Mathematics” course is offered through MIT’s OpenCourseWare, which includes lectures, notes and problem sets.  In addition, Mahajan has made the book available for free in PDF format.

Yet Another Way to Lie With Statistics

This is a nice takedown of some spurious economic analysis, courtesy of Freakonomics:

http://www.freakonomics.com/2011/03/30/how-to-spot-advocacy-science-john-taylor-edition/

Looking at the graph at the right, it’s hard not notice the negative correlation between the two given variables, and the economist in question uses that correlation to bolster his policy argument.

The graph looks a lot different, however, when you look at all the available data, not just the data between today and the arbitrarily chosen cut-off of 1990.  But that chart doesn’t support the argument as decisively.

As the author suggests, “Be wary of economists wielding short samples.”

Math and Computer Animation

This is a clear, concise, and fascinating overview of how some very advanced mathematical ideas are making their way into 3-D animation.

http://www1.ams.org/samplings/feature-column/fcarc-harmonic

Here’s the basic setup.   In order to efficiently model a character, you approximate it with a frame that is built around a few important points.  To move the character, you focus on moving just those points that define the frame.  Thus, moving the character from point A to point B boils down to understanding where those handful of crucial points go.

The tricky part is figuring out a way to smoothly bring all those in-between points along for the ride, and that’s where the math comes in.  The secret is to think of those in-between points as averages of the points that define the frame.  The article explains how barycentric coordinates, harmonic functions. and a surprising amount of calculus are being used to pull off this movie magic!

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