JacobiAM - The Jacobi amplitude function am
JacobiSN, ..., JacobiDC - The Jacobi elliptic functions sn, ..., dc
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Calling Sequence
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JacobiAM(z, k)
JacobiCD(z, k), JacobiCN(z, k), JacobiCS(z, k),
JacobiDC(z, k), JacobiDN(z, k), JacobiDS(z, k),
JacobiNC(z, k), JacobiND(z, k), JacobiNS(z, k),
JacobiSC(z, k), JacobiSD(z, k), JacobiSN(z, k)
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Parameters
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z
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algebraic expression
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k
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algebraic expression, the modulus of the elliptic function
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Description
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The JacobiAM and the twelve JacobiPQ functions, where P and Q are any two of {C,D,N,S}, are inverses of elliptic integrals and doubly periodic elliptic functions. All JacobiPQ satisfy where P, Q, R are any three of {C,D,N,S}. Hence, all JacobiPQ can be defined in terms of the three {JacobiSN, JacobiCN, JacobiDN }.
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The three JacobiSN, JacobiCN and JacobiDN are in turn defined in terms of the amplitude function JacobiAM.
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The JacobiDN function is also sometimes defined as a function of JacobiAM indirectly, through JacobiSN or JacobiCN, via:
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JacobiDN(z,k)^2 = 1-k^2*JacobiSN(z,k)^2;
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| (1) |
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JacobiDN(k*z,(1/(k^2))^(1/2)) = JacobiCN(z,k);
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| (2) |
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For , the amplitude function JacobiAM(phi,k) is the inverse of the normal trigonometric form of the incomplete elliptic integral of the first kind, represented in Maple by the InverseJacobiAM function (see G&R, 8.111, 8.141, and A&S 16.1.3, 17.2.6):
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F_trig := FunctionAdvisor( definition, InverseJacobiAM(phi,k))[1];
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FunctionAdvisor( definition, JacobiAM(phi,k));
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The JacobiPQ functions are well described in the "Table of Integrals Series and Products", Gradshteyn and Ryzhik (G&R) and in the popular "Handbook of Mathematical Functions" edited by Abramowitz and Stegun (A&S). In A&S, these functions are expressed in terms of a parameter m, representing the square of the modulus k entering the definition of these functions in Maple or G&R. So, for example, the formula appears in A&S as .
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It is worth noting here the difference between this normal trigonometric form and the Legendre normal form of this elliptic integral (see A&S 17.2.7), in Maple represented by the EllipticF function and with the square root in the denominator split.
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| (5) |
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(5) = convert((5), Int);
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For the general relationship between these two forms of the incomplete elliptic integral of the first kind see EllipticF and InverseJacobiAM.
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The inverse functions for the JacobiPQ are the InverseJacobiPQ functions, all of them (but for JacobiAM) satisfying with no restrictions on the function parameters.
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The JacobiPQ functions are frequently viewed as generalizations of the usual trigonometric functions in that they include all of them as particular cases for ; for instance,
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map(Eval = eval, [JacobiSN(z,k), JacobiCN(z,k), JacobiSC(z,k)], k=0);
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From the above, JacobiSN, JacobiCN, JacobiSC are usually viewed as generalizations of sin, cos, and tan respectively.
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Examples
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For , the JacobiPQ functions become the hyperbolic trigonometric functions.
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Many familiar trigonometric identities are generalizable to identities involving the JacobiPQ, for example,
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The composition of any JacobiPQ with InverseJacobiAM or any of InverseJacobiRS where R, S are one of {C,D,S} leads to elementary forms.
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| (12) |
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In the case of (Inverse)JacobiCN and (Inverse)JacobiSN, the two possible compositions are equal
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| (15) |
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