# Mathematical Digest

### Short Summaries of Articles about Mathematics

in the Popular Press

"Hurricanes and butterflies," by Thomas C. Halsey and Mogens H. Jensen. *Nature*,11 March 2004, pages 127-128.

Systems may seem chaotic, but such a property can be hard to verify. Accordingto the authors of this article, Sam Gratrix and John N. Elgin "have developed apowerful new method to determine from experimental observation of a systemwhether it is chaotic, and, if it is, what the precise quantitative nature ofthat chaos is." Gratrix and Elgin have used recurrence times, the time it takespoints to return within a certain distance of its starting point, to verify themultifractal properties of strange attractors. The new method is preferable tothe "box-counting" method, which can classify non-multifractals asmultifractals. The research is published in *Physical Review Letters*, "Pointwise Dimensions of the LorenzAttractor."

*--- Mike Breen*