“Pythagorean means”的意思、由来-开放百科全书

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Pythagorean means

释义

Definition
Properties
Inequalities among means
See also
References
External links

In mathematics, the three classical Pythagorean means are the arithmetic mean (AM), the geometric mean (GM), and the harmonic mean (HM). These means were studied with proportions by Pythagoreans and later generations of Greek mathematicians^[1] because of their importance in geometry and music.

Definition

They are defined by:

Properties

Each mean, , has the following properties:

Value preservation

First order: //homogeneous function">homogeneity:

Invariance under exchange

for any and .

Averaging

The harmonic and arithmetic means are reciprocal duals of each other for positive arguments:

while the geometric mean is its own reciprocal dual:

Inequalities among means

There is an ordering to these means (if all of the are positive)

with equality holding if and only if the are all equal.

This is a generalization of the inequality of arithmetic and geometric means and a special case of an inequality for generalized means. The proof follows from the arithmetic-geometric mean inequality, , and reciprocal duality ( and are also reciprocal dual to each other).

The study of the Pythagorean means is closely related to the study of majorization and Schur-convex functions. The harmonic and geometric means are concave symmetric functions of their arguments, and hence Schur-concave, while the arithmetic mean is a linear function of its arguments, so both concave and convex.

References

1. ^{{cite book|first=Thomas|last=Heath|title=History of Ancient Greek Mathematics}}

External links

{{MathWorld|urlname=PythagoreanMeans|title=Pythagorean Means|author=Cantrell, David W.}}
Nice comparison of Pythagorean means with emphasis on the harmonic mean.

1 : Means

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Definition

Properties

Inequalities among means

See also

References

External links