3.5.2.5.30 Jacobian_theta

Definition:

The y = jacobian_theta(k, x, q) computes the value of one of the Jacobian theta functions \theta _0 (x, q), \theta _1 (x, q), \theta _2 (x, q), \theta _3 (x, q) or \theta _4 (x, q) for a real argument x and non-negative q ≤ 1.

The routine evaluates an approximation to the Jacobian theta functions \theta _0 (x, q), \theta _1 (x, q), \theta _2 (x, q), \theta _3 (x, q) and \theta _4 (x, q) given by

\theta _0\left( x,q\right) =1+2\sum_{n=1}^\infty \left( -1\right) ^nq^{n^2}\cos (2n\pi x),
\theta _1\left( x,q\right) =2\sum_{n=0}^\infty \left( -1\right)^nq^{(n+0.5)^2}\sin((2n+1)\pi x),
\theta _2\left( x,q\right) =2\sum_{n=0}^\infty q^{(n+0.5)^2}\cos ((2n+1)\pi x),
\theta _3\left( x,q\right) =1+2\sum_{n=1}^\infty q^{n^2}\cos (2n\pi x),
\theta _4\left( x,q\right) =\theta _0\left( x,q\right),

where x and q are real with 0 ≤ q ≤ 1. Note that \theta _1 (x-0.5, 1) is undefined if (x-0.5) is an integer, as is \theta _2 (x, 1) if x is an integer. Otherwise, \theta _i (x, 1)=0, for i=0, 1, ..., 4.

For more information please refer to the s21ccc function in the NAG document.

Parameters:

k (input, integer)
The function \theta _k (x,q) to be evaluated. Note that k=4 is equivalent to k=0.
Constraint: 0 ≤ k ≤ 4.
x (input, double)
The argument x of the function.
Constraints: x must not be an integer when q=1.0 and k=2; (x-0.5) must not be an integer when q=1.0 and k=1.
q (input, double)
The argument q of the function.
Constraint: 0.0 ≤ q ≤ 1.0.
y (output, double)
The return value of one of the Jacobian theta functions.