# Legendre function

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In mathematics, the **Legendre functions** *P*_{λ}, *Q*_{λ} and **associated Legendre functions** *P*Template:Su, *Q*Template:Su are generalizations of Legendre polynomials to non-integer degree.

## Differential equation

Associated Legendre functions are solutions of the **general Legendre equation**

where the complex numbers λ and μ are called the degree and order of the associated Legendre functions, respectively. The Legendre polynomials are the associated Legendre functions of order μ=0.

This is a second order linear equation with three regular singular points (at 1, −1, and ∞). Like all such equations, it can be converted into a hypergeometric differential equation by a change of variable, and its solutions can be expressed using hypergeometric functions.

## Definition

These functions may actually be defined for general complex parameters and argument:

where is the gamma function and is the hypergeometric function.

The second order differential equation has a second solution, , defined as:

## Integral representations

The Legendre functions can be written as contour integrals. For example

where the contour circles around the points 1 and *z* in the positive direction and does not circle around −1.
For real x, we have

## Legendre function as characters

The real integral representation of are very useful in the study of harmonic analysis on where is the double coset space of (see Zonal spherical function). Actually the Fourier transform on is given by

where

## References

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## External links

- Legendre function P on the Wolfram functions site.
- Legendre function Q on the Wolfram functions site.
- Associated Legendre function P on the Wolfram functions site.
- Associated Legendre function Q on the Wolfram functions site.