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The geometric mean can also be expressed as the exponential of the arithmetic mean of logarithms. [4] By using logarithmic identities to transform the formula, the multiplications can be expressed as a sum and the power as a multiplication:
The logarithmic mean of two numbers is smaller than the arithmetic mean and the generalized mean with exponent greater than 1. However, it is larger than the geometric mean and the harmonic mean, respectively. The inequalities are strict unless both numbers are equal.
The power mean could be generalized further to the generalized f-mean: (, …,) = (= ()) This covers the geometric mean without using a limit with f(x) = log(x). The power mean is obtained for f(x) = x p. Properties of these means are studied in de Carvalho (2016).
In mathematics, the arithmetic–geometric mean (AGM or agM [1]) of two positive real numbers x and y is the mutual limit of a sequence of arithmetic means and a sequence of geometric means. The arithmetic–geometric mean is used in fast algorithms for exponential , trigonometric functions , and other special functions , as well as some ...
is the minimum. (,) is the geometric mean.(,) is the logarithmic mean.It can be obtained from the mean value theorem by choosing () = . (,) is the power mean with exponent .(,) is the identric mean.
In general, logarithms can be calculated using power series or the arithmetic–geometric mean, or be retrieved from a precalculated logarithm table that provides a fixed precision. [ 45 ] [ 46 ] Newton's method , an iterative method to solve equations approximately, can also be used to calculate the logarithm, because its inverse function, the ...
Logarithms can be used to make calculations easier. For example, two numbers can be multiplied just by using a logarithm table and adding. These are often known as logarithmic properties, which are documented in the table below. [2] The first three operations below assume that x = b c and/or y = b d, so that log b (x) = c and log b (y) = d.
The computational complexity of computing the natural logarithm using the arithmetic-geometric mean (for both of the above methods) is (() ). Here, n is the number of digits of precision at which the natural logarithm is to be evaluated, and M ( n ) is the computational complexity of multiplying two n -digit numbers.