NAG Library Function Document

nag_real_jacobian_elliptic (s21cac)

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: u – doubleInput

2: m – doubleInput

On entry: the argument

u

and the argument

m

of the functions, respectively.

Constraints:

$abs (u) \leq \sqrt{λ}$ , where $λ = 1 / nag_real_safe_small_number$ ;
if $abs (u) < 1 / \sqrt{λ}$ , $abs (m) \leq \sqrt{λ}$ .

3: sn – double *Output

4: cn – double *Output

5: dn – double *Output

On exit: the values of the functions

sn u

cn u

and

dn u

, respectively.

6: fail – NagError *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, $|m|$ is too large when used in conjunction with the supplied argument u: $|m| = ⟨value⟩$ it must be less than $⟨value⟩$ .
On entry, $|u|$ is too large: $|u| = ⟨value⟩$ 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 Parallelism and Performance

Not applicable.

9 Further Comments

None.

10 Example

This example reads values of the argument

u

and argument

m

from a file, evaluates the function and prints the results.

NAG Library Function Documentnag_real_jacobian_elliptic (s21cac)

+− Contents

1 Purpose

2 Specification

3 Description