In physical science and mathematics, the Legendre functions , and associated Legendre functions , , and Legendre functions of the second kind, , are all solutions of Legendre's differential equation. The
Legendre polynomials
In physical science and mathematics, Legendre polynomials (named after Adrien-Marie Legendre, who discovered them in 1782) are a system of complete and orthogonal polynomials, with a vast number of mathematical properties, and numerous applicat ...
and the
associated Legendre polynomials are also solutions of the differential equation in special cases, which, by virtue of being polynomials, have a large number of additional properties, mathematical structure, and applications. For these polynomial solutions, see the separate Wikipedia articles.
Legendre's differential equation
The general Legendre equation reads
where the numbers and may be complex, and are called the degree and order of the relevant function, respectively. The polynomial solutions when is an integer (denoted ), and are the Legendre polynomials ; and when
is an integer (denoted ), and is also an integer with are the associated Legendre polynomials. All other cases of and can be discussed as one, and the solutions are written , . If , the superscript is omitted, and one writes just , . However, the solution when is an integer is often discussed separately as Legendre's function of the second kind, and denoted .
This is a second order linear equation with three regular singular points (at , , 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.
Solutions of the differential equation
Since the differential equation is linear, homogeneous (the right hand side =zero) and of second order, it has two linearly independent solutions, which can both be expressed in terms of the
hypergeometric function,
. With
being the
gamma function
In mathematics, the gamma function (represented by , the capital letter gamma from the Greek alphabet) is one commonly used extension of the factorial function to complex numbers. The gamma function is defined for all complex numbers except ...
, the first solution is
and the second is,
These are generally known as Legendre functions of the first and second kind of noninteger degree, with the additional qualifier 'associated' if is non-zero. A useful relation between the and solutions is
Whipple's formula.
Legendre functions of the second kind ()
The nonpolynomial solution for the special case of integer degree
, and
, is often discussed separately.
It is given by
This solution is necessarily
singular
Singular may refer to:
* Singular, the grammatical number that denotes a unit quantity, as opposed to the plural and other forms
* Singular homology
* SINGULAR, an open source Computer Algebra System (CAS)
* Singular or sounder, a group of boar, ...
when
.
The Legendre functions of the second kind can also be defined recursively via
Bonnet's recursion formula
Associated Legendre functions of the second kind
The nonpolynomial solution for the special case of integer degree
, and
is given by
Integral representations
The Legendre functions can be written as contour integrals. For example,
where the contour winds around the points and in the positive direction and does not wind around .
For real , 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
A double is a look-alike or doppelgänger; one person or being that resembles another.
Double, The Double or Dubble may also refer to:
Film and television
* Double (filmmaking), someone who substitutes for the credited actor of a character
* ...
of
(see
Zonal spherical function In mathematics, a zonal spherical function or often just spherical function is a function on a locally compact group ''G'' with compact subgroup ''K'' (often a maximal compact subgroup) that arises as the matrix coefficient of a ''K''-invariant vect ...
). Actually the Fourier transform on
is given by
where
See also
*
Ferrers function
References
*
* .
*
*
*
*
External links
Legendre function Pon the Wolfram functions site.
Legendre function Qon the Wolfram functions site.
Associated Legendre function Pon the Wolfram functions site.
Associated Legendre function Qon the Wolfram functions site.
{{Authority control
Hypergeometric functions