British Association for the Advancement of Science: Home-made computer cuts bigger slice of pi

A MATHEMATICAL problem that has dogged thinkers for 4,000 years has come close to being solved by two New York brothers on their home-made computer writes Steve Connor.

David and Gregory Chudnovsky have worked out the value of the mathematical constant pi - the ratio of a circle's circumference to its diameter - to 2.16 billion decimal places, a number long enough to fill 20 encyclopaedias.

Their computer, built at a cost of dollars 70,000 with the help of money from their wives and a grant from Columbia University, has 25 fans to prevent it melting when number crunching.

Although it is a world record for computing the value of pi, mathematicians believe that it is not the end of the story that began 2,000 years ago in Babylonia. Peter Webster, a mathematician at the University of Sheffield, told the British Association's annual meeting yesterday that the exact value of pi, which is about 3.14, will be the subject of intrigue for years to come.

For thousands of years, mathematicians came gradually closer to calculating the precise value of pi, Archimedes setting the standard in 240BC.

The constant did not have a universally recognised name until a Welshman, William Jones, wrote a mathematical treatise and referred to the number as pi. 'The book was on the top-selling list for year after year. Jones was like Stephen Hawking in his popularity,' Dr Webster said.

In 1840, a German boy, Johann Dase, calculated pi to 200 decimal places in his head. Dr Webster said his computing genius earned him a considerable reputation. 'He was a human calculator.'

Other attempts at mentally calculating the exact value of pi were quickly superseded by the first electronic attempt on the ENIAC computer in 1949.

Two French mathematicians calculated it to a million decimal places in the early Seventies. In 1989, a Japanese managed to break through the billion decimal place barrier.

Dr Webster is adamant that the latest attempt will not be the end of the matter. The continuing saga of calculating pi 'is to be continued'.