Definition:Legendre's Standard Elliptic Integrals

Special Function

$\ds \map F {k, \phi} = \int \limits_0^x \frac {\d v} {\sqrt {\paren {1 - v^2} \paren {1 - k^2 v^2} } }$

is the incomplete elliptic integral of the first kind, and is a function of the variables:

$k$, defined on the interval $0 < k < 1$

$x = \sin \phi$, where $\phi$ is defined on the interval $0 \le \phi \le \pi / 2$.

$\ds \map E {k, \phi} = \int \limits_0^x \dfrac {\sqrt {1 - k^2 v^2} } {\sqrt {1 - v^2}} \rd v$

is the incomplete elliptic integral of the second kind, and is a function of the variables:

$k$, defined on the interval $0 < k < 1$

$x = \sin \phi$, where $\phi$ is defined on the interval $0 \le \phi \le \pi / 2$.

$\ds \map \Pi {k, n, \phi} = \int \limits_0^x \frac {\d v} {\paren {1 + n v^2} \sqrt {\paren {1 - v^2} \paren {1 - k^2 v^2} } }$

is the incomplete elliptic integral of the third kind, and is a function of the variables:

$k$, defined on the interval $0 < k < 1$

$n \in \Z$

$x = \sin \phi$, where $\phi$ is defined on the interval $0 \le \phi \le \pi / 2$.

This entry was named for Adrien-Marie Legendre.

The elliptic integrals were called that because they were first encountered in the problem of determining the length of the perimeter of an ellipse.