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Difference between revisions of "Modulus of an elliptic integral"

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The parameter <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064560/m0645601.png" /> which enters into the expression of the [[Elliptic integral|elliptic integral]] in Legendre normal form. For example, in the incomplete elliptic integral of the first kind,
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The parameter $k$ which enters into the expression of the [[Elliptic integral|elliptic integral]] in Legendre normal form. For example, in the incomplete elliptic integral of the first kind,
  
<table class="eq" style="width:100%;"> <tr><td valign="top" style="width:94%;text-align:center;"><img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064560/m0645602.png" /></td> <td valign="top" style="width:5%;text-align:right;">(*)</td></tr></table>
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$$F(\phi,k)=\int_0^\phi\frac{dt}{\sqrt{1-k^2\sin^2t}}.\tag{*}$$
  
The number <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064560/m0645603.png" /> is sometimes called the Legendre modulus, <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064560/m0645604.png" /> is called the complementary modulus. In applications the normal case <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064560/m0645605.png" /> usually holds; here the sharp angle <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064560/m0645606.png" /> for which <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064560/m0645607.png" /> is called the modular angle. The modulus <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064560/m0645608.png" /> also enters into the expression of the [[Jacobi elliptic functions|Jacobi elliptic functions]], which arise from the inversion of elliptic integrals of the form (*).
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The number $k^2$ is sometimes called the Legendre modulus, $k'=\sqrt{(1-k^2)}$ is called the complementary modulus. In applications the normal case $0<k<1$ usually holds; here the sharp angle $\theta$ for which $\sin\theta=k$ is called the modular angle. The modulus $k$ also enters into the expression of the [[Jacobi elliptic functions|Jacobi elliptic functions]], which arise from the inversion of elliptic integrals of the form \ref{*}.
  
  

Revision as of 13:05, 9 August 2014

The parameter $k$ which enters into the expression of the elliptic integral in Legendre normal form. For example, in the incomplete elliptic integral of the first kind,

$$F(\phi,k)=\int_0^\phi\frac{dt}{\sqrt{1-k^2\sin^2t}}.\tag{*}$$

The number $k^2$ is sometimes called the Legendre modulus, $k'=\sqrt{(1-k^2)}$ is called the complementary modulus. In applications the normal case $0<k<1$ usually holds; here the sharp angle $\theta$ for which $\sin\theta=k$ is called the modular angle. The modulus $k$ also enters into the expression of the Jacobi elliptic functions, which arise from the inversion of elliptic integrals of the form \ref{*}.


Comments

References

[a1] F. Bowman, "Introduction to elliptic functions with applications" , Dover, reprint (1961)
How to Cite This Entry:
Modulus of an elliptic integral. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Modulus_of_an_elliptic_integral&oldid=15159
This article was adapted from an original article by E.D. Solomentsev (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article