The BBP Algorithm for Pi

Technical Report · Sun Sep 17 04:00:00 EDT 2006

DOI:https://doi.org/10.2172/983322· OSTI ID:983322

Bailey, David H

The 'Bailey-Borwein-Plouffe' (BBP) algorithm for {pi} is based on the BBP formula for {pi}, which was discovered in 1995 and published in 1996 [3]: {pi} = {summation}{sub k=0}{sup {infinity}} 1/16{sup k} (4/8k+1 - 2/8k+4 - 1/8k+5 - 1/8k+6). This formula as it stands permits {pi} to be computed fairly rapidly to any given precision (although it is not as efficient for that purpose as some other formulas that are now known [4, pg. 108-112]). But its remarkable property is that it permits one to calculate (after a fairly simple manipulation) hexadecimal or binary digits of {pi} beginning at an arbitrary starting position. For example, ten hexadecimal digits {pi} beginning at position one million can be computed in only five seconds on a 2006-era personal computer. The formula itself was found by a computer program, and almost certainly constitutes the first instance of a computer program finding a significant new formula for {pi}. It turns out that the existence of this formula has implications for the long-standing unsolved question of whether {pi} is normal to commonly used number bases (a real number x is said to be b-normal if every m-long string of digits in the base-b expansion appears, in the limit, with frequency b{sup -m}). Extending this line of reasoning recently yielded a proof of normality for class of explicit real numbers (although not yet including {pi}) [4, pg. 148-156].

• Research Organization: Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US)
• Sponsoring Organization: Computational Research Division
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 983322
• Report Number(s): LBNL-3481E
• Country of Publication: United States
• Language: English

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