# Mathematical Digest

### Short Summaries of Articles about Mathematics

in the Popular Press

"Coming Up Trumps," by Erica Klarreich. *New Scientist,* 20 July 2002,pages 42-44.

How well does the card-shuffling machine shuffle cards? When a Las Vegascasino company wanted to find out, it asked mathematician and magician PersiDiaconis of Stanford University. Diaconis and Susan Holmes, a Stanfordstatistician, analyzed the machine and found that the machine did not mix thecards well enough. Their strategy for guessing the order of some of the cardsin a machine-shuffled deck "was enough to unsettle the company engineers,"Klarreich writes. The engineers are now trying to figure out how to correctthis problem. Surprisingly, the method the machines use, called "shelfshuffling," has a link to noncommutative geometry, which arises in quantummechanics.

*--- Allyn Jackson*