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The geometric series is an infinite series derived from a special type of sequence called a geometric progression.This means that it is the sum of infinitely many terms of geometric progression: starting from the initial term , and the next one being the initial term multiplied by a constant number known as the common ratio .
It repeatedly replaces two numbers by their arithmetic and geometric mean, in order to approximate their arithmetic-geometric mean. The version presented below is also known as the Gauss–Euler, Brent–Salamin (or Salamin–Brent) algorithm; [1] it was independently discovered in 1975 by Richard Brent and Eugene Salamin.
In mathematics, a series is, roughly speaking, an addition of infinitely many terms, one after the other. [1] The study of series is a major part of calculus and its generalization, mathematical analysis. Series are used in most areas of mathematics, even for studying finite structures in combinatorics through generating functions.
In more recent years, computer programs have been used to find and calculate more precise approximations of the perimeter of an ellipse. In an online video about the perimeter of an ellipse, recreational mathematician and YouTuber Matt Parker , using a computer program, calculated numerous approximations for the perimeter of an ellipse. [ 10 ]
In 1706, John Machin used Gregory's series (the Taylor series for arctangent) and the identity = to calculate 100 digits of π (see § Machin-like formula below). [ 30 ] [ 31 ] In 1719, Thomas de Lagny used a similar identity to calculate 127 digits (of which 112 were correct).
where C is the circumference of an ellipse with semi-major axis a and semi-minor axis b and , are the arithmetic and geometric iterations of (,), the arithmetic-geometric mean of a and b with the initial values = and =.
Comparison of the convergence of the Wallis product (purple asterisks) and several historical infinite series for π. S n is the approximation after taking n terms. Each subsequent subplot magnifies the shaded area horizontally by 10 times. (click for detail) The Wallis product is the infinite product representation of π:
An infinite series of any rational function of can be reduced to a finite series of polygamma functions, by use of partial fraction decomposition, [8] as explained here. This fact can also be applied to finite series of rational functions, allowing the result to be computed in constant time even when the series contains a large number of terms.