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Elliptic Alpha Function


The elliptic alpha function alpha(r), defined for r>0, relates the complete elliptic integrals of the first K(k_r) and second kinds E(k_r) at elliptic integral singular values k_r according to

alpha(r)=(E^'(k_r))/(K(k_r))-pi/(4[K(k_r)]^2)
(1)
=pi/(4[K(k_r)]^2)+sqrt(r)-(E(k_r)sqrt(r))/(K(k_r))
(2)
=(pi^(-1)-4sqrt(r)q(dtheta_4(q))/(dq)1/(theta_4(q)))/(theta_3^4(q)),
(3)

where k_r=lambda^*(r), q=e^(-pisqrt(r)), lambda^*(r) is the elliptic lambda function, and theta_3(q) and theta_4(q) are Jacobi theta functions. Here K(k) and E(k) use the elliptic modulus k, and E^'(k)=E(sqrt(1-k^2)) is the complementary complete elliptic integral of the second kind. The elliptic alpha function is related to the elliptic delta function by

 alpha(r)=1/2[sqrt(r)-delta(r)].
(4)

It satisfies

 alpha(4r)=(1+k_(4r))^2alpha(r)-2sqrt(r)k_(4r),
(5)

and has the asymptotic behavior

 alpha(r)-1/pi∼8(sqrt(r)-1/pi)e^(-pisqrt(r))
(6)

as r->infty (Borwein et al. 1989). A few specific values (Borwein and Borwein 1987, p. 172) are

alpha(1)=1/2
(7)
alpha(2)=sqrt(2)-1
(8)
alpha(3)=1/2(sqrt(3)-1)
(9)
alpha(4)=2(sqrt(2)-1)^2
(10)
alpha(5)=1/2(sqrt(5)-sqrt(2sqrt(5)-2))
(11)
alpha(6)=5sqrt(6)+6sqrt(3)-8sqrt(2)-11
(12)
alpha(7)=1/2(sqrt(7)-2)
(13)
alpha(8)=2(10+7sqrt(2))(1-sqrt(sqrt(8)-2))^2
(14)
alpha(9)=1/2[3-3^(3/4)sqrt(2)(sqrt(3)-1)]
(15)
alpha(10)=-103+72sqrt(2)-46sqrt(5)+33sqrt(10)
(16)
alpha(12)=264+154sqrt(3)-188sqrt(2)-108sqrt(6)
(17)
alpha(13)=1/2(sqrt(13)-sqrt(74sqrt(13)-258))
(18)
alpha(15)=1/2(sqrt(15)-sqrt(5)-1)
(19)
alpha(16)=(4(sqrt(8)-1))/((2^(1/4)+1)^4)
(20)
alpha(18)=-3057+2163sqrt(2)+1764sqrt(3)-1248sqrt(6)
(21)
alpha(22)=-12479-8824sqrt(2)+3762sqrt(11)+2661sqrt(22)
(22)
alpha(25)=5/2[1-25^(1/4)(7-3sqrt(5))]
(23)
alpha(27)=3[1/2(sqrt(3)+1)-2^(1/3)]
(24)
alpha(30)=1/2{sqrt(30)-(2+sqrt(5))^2(3+sqrt(10))^2(-6-5sqrt(2)-3sqrt(5)-2sqrt(10)+sqrt(6)sqrt(57+40sqrt(2)))[56+38sqrt(2)+sqrt(30)(2+sqrt(5))(3+sqrt(10))]}
(25)
alpha(37)=1/2[sqrt(37)-(171-25sqrt(37))sqrt(sqrt(37)-6)]
(26)
alpha(46)=1/2[sqrt(46)+(18+13sqrt(2)+sqrt(661+468sqrt(2)))^2(18+13sqrt(2)-3sqrt(2)sqrt(147+104sqrt(2))+sqrt(661+468sqrt(2)))(200+14sqrt(2)+26sqrt(23)+18sqrt(46)+sqrt(46)sqrt(661+468sqrt(2)))]
(27)
alpha(49)=7/2-sqrt(7[sqrt(2)7^(3/4)(33011+12477sqrt(7))-21(9567+3616sqrt(7))])
(28)
alpha(58)=[1/2(sqrt(29)+5)]^6(99sqrt(29)-444)(99sqrt(2)-70-13sqrt(29))
(29)
=3(-40768961+28828008sqrt(2)-7570606sqrt(29)+5353227sqrt(58))
(30)
alpha(64)=(8[2(sqrt(8)-1)-(2^(1/4)-1)^4])/((sqrt(sqrt(2)+1)+2^(5/8))^4).
(31)

J. Borwein has written an algorithm which uses lattice basis reduction to provide algebraic values for alpha(n).


See also

Elliptic Integral of the First Kind, Elliptic Integral of the Second Kind, Elliptic Integral Singular Value, Elliptic Lambda Function

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References

Borwein, J. M. and Borwein, P. B. Pi & the AGM: A Study in Analytic Number Theory and Computational Complexity. New York: Wiley, 1987.Borwein, J. M.; Borwein, P. B.; and Bailey, D. H. "Ramanujan, Modular Equations, and Approximations to Pi, or How to Compute One Billion Digits of Pi." Amer. Math. Monthly 96, 201-219, 1989.

Referenced on Wolfram|Alpha

Elliptic Alpha Function

Cite this as:

Weisstein, Eric W. "Elliptic Alpha Function." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/EllipticAlphaFunction.html

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