# Lamé equation

A linear ordinary second-order differential equation in the complex domain

$$\tag{1 } \frac{d ^ {2} w }{d z ^ {2} } = \ \left [ A + B {\mathcal p} ( z) \right ] w ,$$

where ${\mathcal p} ( z)$ is the Weierstrass ${\mathcal p}$- function and $A$ and $B$ are constants. This equation was first studied by G. Lamé ; it arises in the separation of variables for the Laplace equation in elliptic coordinates. Equation (1) is also called the Weierstrass form of the Lamé equation. By a change of the independent variable in (1) one obtains Jacobi's form of the Lamé equation:

$$\frac{d ^ {2} w }{d u ^ {2} } = \ \left [ C + D \mathop{\rm sn} ^ {2} u \right ] w .$$

There are also numerous algebraic forms of the Lamé equation, transition to which is carried out by various transformations of the independent variable in (1), for example:

$$\tag{2 } \frac{d ^ {2} w }{d \xi ^ {2} } + \frac{1}{2} \left ( \frac{1}{\xi - e _ {1} } + \frac{1}{\xi - e _ {2} } + \frac{1}{\xi - e _ {3} } \right ) \frac{dw}{d \xi } =$$

$$= \ \frac{A + B \xi }{4 ( \xi - e _ {1} ) ( \xi - e _ {2} ) ( \xi - e _ {3} ) } w .$$

For practical applications the Jacobi form is the most suitable.

Especially important is the case when in (1) (or (2)) $B = n ( n + 1 )$, where $n$ is a natural number. In this case the solutions of (1) are meromorphic in the whole plane and their properties have been thoroughly studied. Among the solutions of (2) with $B = n ( n + 1 )$ the Lamé functions are of paramount importance (cf. Lamé function).

How to Cite This Entry:
Lamé equation. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Lam%C3%A9_equation&oldid=47571
This article was adapted from an original article by N.Kh. Rozov (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article