nag_real_jacobian_elliptic (s21cac) (PDF version)
s Chapter Contents
s Chapter Introduction
NAG C Library Manual

NAG Library Function Document

nag_real_jacobian_elliptic (s21cac)

+ Contents

    1  Purpose
    7  Accuracy

1  Purpose

nag_real_jacobian_elliptic (s21cac) evaluates the Jacobian elliptic functions sn, cn and dn.

2  Specification

#include <nag.h>
#include <nags.h>
void  nag_real_jacobian_elliptic (double u, double m, double *sn, double *cn, double *dn, NagError *fail)

3  Description

nag_real_jacobian_elliptic (s21cac) evaluates the Jacobian elliptic functions of argument u and argument m,
snum = sinϕ, cnum = cosϕ, dnum = 1-msin2ϕ,
where ϕ, called the amplitude of u, is defined by the integral
u=0ϕdθ 1-msin2θ .
The elliptic functions are sometimes written simply as snu, cnu and dnu, avoiding explicit reference to the argument m.
Another nine elliptic functions may be computed via the formulae
cdu = cnu/dnu sdu = snu/dnu ndu = 1/dnu dcu = dnu/cnu ncu = 1/cnu scu = snu/cnu nsu = 1/snu dsu = dnu/snu csu = cnu/snu
(see Abramowitz and Stegun (1972)).
nag_real_jacobian_elliptic (s21cac) is based on a procedure given by Bulirsch (1960), and uses the process of the arithmetic-geometric mean (16.9 in Abramowitz and Stegun (1972)). Constraints are placed on the values of u and m in order to avoid the possibility of machine overflow.

4  References

Abramowitz M and Stegun I A (1972) Handbook of Mathematical Functions (3rd Edition) Dover Publications
Bulirsch R (1960) Numerical calculation of elliptic integrals and elliptic functions Numer. Math. 7 76–90

5  Arguments

1:     udoubleInput
2:     mdoubleInput
On entry: the argument u and the argument m of the functions, respectively.
Constraints:
  • absu λ , where λ = 1 / nag_real_safe_small_number;
  • if absu < 1 / λ , absm λ .
3:     sndouble *Output
4:     cndouble *Output
5:     dndouble *Output
On exit: the values of the functions snu, cnu and dnu, respectively.
6:     failNagError *Input/Output
The NAG error argument (see Section 3.6 in the Essential Introduction).

6  Error Indicators and Warnings

NE_BAD_PARAM
On entry, argument value had an illegal value.
NE_INTERNAL_ERROR
An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please contact NAG for assistance.
NE_REAL_2
On entry, absm is too large when used in conjunction with the supplied argument u: absm=value it must be less than value.
On entry, absu is too large: absu=value it must be less than value.

7  Accuracy

In principle the function is capable of achieving full relative precision in the computed values. However, the accuracy obtainable in practice depends on the accuracy of the standard elementary functions such as SIN and COS.

8  Further Comments

None.

9  Example

This example reads values of the argument u and argument m from a file, evaluates the function and prints the results.

9.1  Program Text

Program Text (s21cace.c)

9.2  Program Data

Program Data (s21cace.d)

9.3  Program Results

Program Results (s21cace.r)


nag_real_jacobian_elliptic (s21cac) (PDF version)
s Chapter Contents
s Chapter Introduction
NAG C Library Manual

© The Numerical Algorithms Group Ltd, Oxford, UK. 2012