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Complete Elliptic Integral of the Second Kind
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EllipticE
EllipticEReIm
EllipticEContours

The complete elliptic integral of the second kind, illustrated above as a function of k, is defined by

E(k)=E(1/2pi,k)
(1)
=pi/2{1-sum_(n=1)^(infty)[((2n-1)!!)/((2n)!!)]^2(k^(2n))/(2n-1)}
(2)
=1/2pi_2F_1(-1/2,1/2;1;k^2)
(3)
=int_0^(K(k))dn^2(u,k)du,
(4)

where E(phi,k) is an incomplete elliptic integral of the second kind, _2F_1(a,b;c;x) is the hypergeometric function, and dn(u,k) is a Jacobi elliptic function.

It is implemented in Mathematica as EllipticE[m], where m=k^2 is the parameter.

E(k) can be computed in closed form in terms of K(k_n) and the elliptic alpha function alpha(n) for special values of k=k_n, where k_n is a called an elliptic integral singular value. Other special values include

E(0)=1/2pi
(5)
E(1)=1.
(6)

The complete elliptic integral of the second kind satisfies the Legendre relation

 E(k)K^'(k)+E^'(k)K(k)-K(k)K^'(k)=1/2pi,
(7)

where K(k) and E(k) are complete elliptic integrals of the first and second kinds, respectively, and K^'(k) and E^'(k) are the complementary integrals. The derivative is

 (dE)/(dk)=(E(k)-K(k))/k
(8)

(Whittaker and Watson 1990, p. 521).

EllipticEODE

The solution to the differential equation

 k^('2)d/(dk)(k(dy)/(dk))+ky=0
(9)

(Zwillinger 1997, p. 122; Gradshteyn and Ryzhik 2000, p. 907) is given by

 y=C_1E(k)+C_2[E^'(k)-K^'(k)].
(10)

If k_r is a singular value (i.e.,

 k_r=lambda^*(r),
(11)

where lambda^* is the elliptic lambda function), and K(k_r) and the elliptic alpha function alpha(r) are also known, then

 E(k)=(K(k))/(sqrt(r))[pi/(3[K(k)]^2)-alpha(r)]+K(k).
(12)

SEE ALSO: Complete Elliptic Integral of the First Kind, Complete Elliptic Integral of the Third Kind, Elliptic Alpha Function, Elliptic Integral of the Second Kind, Elliptic Integral Singular Value

RELATED WOLFRAM SITES: http://functions.wolfram.com/EllipticIntegrals/EllipticE/

REFERENCES:

Gradshteyn, I. S. and Ryzhik, I. M. Tables of Integrals, Series, and Products, 6th ed. San Diego, CA: Academic Press, 2000.

Whittaker, E. T. and Watson, G. N. A Course in Modern Analysis, 4th ed. Cambridge, England: Cambridge University Press, 1990.

Zwillinger, D. Handbook of Differential Equations, 3rd ed. Boston, MA: Academic Press, p. 122, 1997.




CITE THIS AS:

Weisstein, Eric W. "Complete Elliptic Integral of the Second Kind." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/CompleteEllipticIntegraloftheSecondKind.html

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