#### Important information regarding the recent AMS power outage.

The transformer that provides electricity to the AMS building in Providence went down on Sunday, April 22. The restoration of our email, website, AMS Bookstore and other systems is almost complete. We are currently running on a generator but overnight a new transformer should be hooked up and (fingers crossed) we should be fine by 8:00 (EDT) Wednesday morning. This issue has affected selected phones, which should be repaired by the end of today. No email was lost, although the accumulated messages are only just now being delivered so you should expect some delay.

Thanks for your patience.

# Mathematical Digest

### Short Summaries of Articles about Mathematics

in the Popular Press

"Passing Messages Between Disciplines," by Marc Mézard. *Science*, 19 September 2003,pages 1685-1686.

The disciplines in this case are physics and computer science---applied toerror-correcting codes---but there is some mathematics in this article. Someerror-correcting systems work in theory but have been impractical to implement.A technique called *belief propagation* can make decoding procedures workfaster so that they are practical. Mézard writes about how beliefpropagation procedures are applied to the satisfiability problem (whether thereexist truth values for a set of Boolean variables so that given constraints aresatisfied). Satisfiability has a critical value, separating problems that arealmost always satisfiable from those that are almost never satisfiable.Statistical physics helps to understand the phase transition between the twoopposite regions of problems, which helps improve belief propagationprocedures.

*--- Mike Breen*