Pi continued.

It's possible to use the distribution of bright stars across the night sky to deduce a numerical value of pi ([pi]) that comes within 0.5 percent of its exact value (SN: 5/20/95, p.319). But determining pi--the ratio of the circumference of a circle to its diameter--to billions of decimal places requires mathematical ingenuity and tremendous computer power.

Earlier this month, Yasumasa Kanada and his coworkers at the University of Tokyo announced that they had calculated pi to 3.22 billion decimal places, beating the old record of 2.26 billion digits (SN: 8/24/91, p.127). The researchers checked their result by using two different formulas to compute pi, requiring more than 36 hours to complete each calculation on a supercomputer.

Meanwhile, mathematicians David V. and Gregory V. Chudnovsky of Columbia University, who held the old record, have been quietly extending their own calculation. In response to the Japanese announcement, the Chudnovskys noted that they had upgraded their own custom-built computer and had already reached more than 4 billion decimal digits of pi last year.

Such calculations of pi involve much more than setting a record. The Chudnovskys, for example, have developed novel mathematical formulas for computing pi efficiently and methods for checking the results to ensure that the digits are correct. Computing pi to a large number of decimal places also serves as an excellent test of how well a computer functions. The Chudnovskys have been able to use their pi-tested computer to complete a variety of mathematical calculations linked to the study of certain types of differential equations.