Interfaces: FL CL AD

s21cb: FL CL AD

NAG CL Interface
s21cbc (jacellip_complex)

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NAG Library Manual, Mark 27

Interfaces: FL CL AD

NAG CL Interface Introduction

S (Specfun) Chapter Contents

S (Specfun) Chapter Introduction

s21cb: FL CL AD

▸▿ Contents

1 Purpose

2 Specification

3 Description

4 References

5 Arguments

6 Error Indicators and Warnings

7 Accuracy

8 Parallelism and Performance

9 Further Comments

▸▿ 10 Example

10.1 Program Text

10.2 Program Data

10.3 Program Results

1 Purpose

s21cbc evaluates the Jacobian elliptic functions

sn z

cn z

and

dn z

for a complex argument

z

2 Specification

#include <nag.h>

void	s21cbc (Complex z, double ak2, Complex sn, Complex cn, Complex dn, NagError fail)

The function may be called by the names: s21cbc, nag_specfun_jacellip_complex or nag_jacobian_elliptic.

3 Description

s21cbc evaluates the Jacobian elliptic functions

sn (z ∣ k)

cn (z ∣ k)

and

dn (z ∣ k)

given by

\begin{array}{lcl} sn (z ∣ k) & = & \sin ϕ \\ cn (z ∣ k) & = & \cos ϕ \\ dn (z ∣ k) & = & \sqrt{1 - k^{2} \sin^{2} ϕ}, \end{array}

where

z

is a complex argument,

k

is a real argument (the modulus) with

k^{2} \leq 1

and

ϕ

(the amplitude of

z

) is defined by the integral

z = \int_{0}^{ϕ} \frac{d θ}{\sqrt{1 - k^{2} \sin^{2} θ}} .

The above definitions can be extended for values of

k^{2} > 1

(see Salzer (1962)) by means of the formulae

\begin{array}{lcl} sn (z ∣ k) & = & k_{1} sn (k z ∣ k_{1}) \\ cn (z ∣ k) & = & dn (k z ∣ k_{1}) \\ dn (z ∣ k) & = & cn (k z ∣ k_{1}), \end{array}

where

k_{1} = 1 / k

Special values include

\begin{array}{lcl} sn (z ∣ 0) & = & \sin z \\ cn (z ∣ 0) & = & \cos z \\ dn (z ∣ 0) & = & 1 \\ sn (z ∣ 1) & = & \tanh z \\ cn (z ∣ 1) & = & sech z \\ dn (z ∣ 1) & = & sech z . \end{array}

These functions are often simply written as

sn z

cn z

and

dn z

, thereby avoiding explicit reference to the argument

k

. They can also be expressed in terms of Jacobian theta functions (see s21ccc).

Another nine elliptic functions may be computed via the formulae

\begin{array}{lcl} cd z & = & cn z / dn z \\ sd z & = & sn z / dn z \\ nd z & = & 1 / dn z \\ dc z & = & dn z / cn z \\ nc z & = & 1 / cn z \\ sc z & = & sn z / cn z \\ ns z & = & 1 / sn z \\ ds z & = & dn z / sn z \\ cs z & = & cn z / sn z \end{array}

(see Abramowitz and Stegun (1972)).

The values of

sn z

cn z

and

dn z

are obtained by calls to s21cac. Further details can be found in Section 9.

4 References

Abramowitz M and Stegun I A (1972) Handbook of Mathematical Functions (3rd Edition) Dover Publications

Salzer H E (1962) Quick calculation of Jacobian elliptic functions Comm. ACM 5 399

5 Arguments

1: $z$ – Complex Input

On entry: the argument

z

of the functions.

Constraints:

$abs (z . re) \leq = \sqrt{λ}$ ;
$abs (z . im) \leq \sqrt{λ}$ , where $λ = 1 / nag_real_safe_small_number$ .

2: $ak2$ – double Input

On entry: the value of

k^{2}

Constraint:

0.0 \leq ak2 \leq 1.0

3: $sn$ – Complex * Output

4: $cn$ – Complex * Output

5: $dn$ – Complex * Output

On exit: the values of the functions

sn z

cn z

and

dn z

, respectively.

6: $fail$ – NagError * Input/Output

The NAG error argument (see Section 7 in the Introduction to the NAG Library CL Interface).

6 Error Indicators and Warnings

NE_ALLOC_FAIL: Dynamic memory allocation failed.
See Section 3.1.2 in the Introduction to the NAG Library CL Interface for further information.
NE_BAD_PARAM: On entry, argument $〈value〉$ had an illegal value.
NE_COMPLEX: On entry, $|z . im|$ is too large: $|z . im| = 〈value〉$ . It must be less than $〈value〉$ .

On entry, $|z . re|$ is too large: $|z . re| = 〈value〉$ . It must be less than $〈value〉$ .
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.
See Section 7.5 in the Introduction to the NAG Library CL Interface for further information.
NE_NO_LICENCE: Your licence key may have expired or may not have been installed correctly.
See Section 8 in the Introduction to the NAG Library CL Interface for further information.
NE_REAL: On entry, $ak2 = 〈value〉$ .
Constraint: $ak2 \leq 1.0$ .

On entry, $ak2 = 〈value〉$ .
Constraint: $ak2 \geq 0.0$ .

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

s21cbc is not threaded in any implementation.

9 Further Comments

The values of

sn z

cn z

and

dn z

are computed via the formulae

\begin{array}{lcccl} sn z & = & \frac{sn (u, k) dn (v, k^{'})}{1 - {dn}^{2} (u, k) {sn}^{2} (v, k^{'})} & + & i \frac{cn (u, k) dn (u, k) sn (v, k^{'}) cn (v, k^{'})}{1 - {dn}^{2} (u, k) {sn}^{2} (v, k^{'})} \\ cn z & = & \frac{cn (u, k) cn (v, k^{'})}{1 - {dn}^{2} (u, k) {sn}^{2} (v, k^{'})} & - & i \frac{sn (u, k) dn (u, k) sn (v, k^{'}) dn (v, k^{'})}{1 - {dn}^{2} (u, k) {sn}^{2} (v, k^{'})} \\ dn z & = & \frac{dn (u, k) cn (v, k^{'}) dn (v, k^{'})}{1 - {dn}^{2} (u, k) {sn}^{2} (v, k^{'})} & - & i \frac{k^{2} sn (u, k) cn (u, k) sn (v, k^{'})}{1 - {dn}^{2} (u, k) {sn}^{2} (v, k^{'})}, \end{array}

where

z = u + i v

and

k^{'} = \sqrt{1 - k^{2}}

(the complementary modulus).

10 Example

This example evaluates

sn z

cn z

and

dn z

z = - 2.0 + 3.0 i

when

k = 0.5

, and prints the results.

Interfaces: FL CL AD

NAG CL Interface Introduction

S (Specfun) Chapter Contents

S (Specfun) Chapter Introduction

s21cb: FL CL AD

NAG CL Interfaces21cbc (jacellip_​complex)

▸▿ Contents

1 Purpose

2 Specification

3 Description

4 References

5 Arguments

6 Error Indicators and Warnings

7 Accuracy

8 Parallelism and Performance

9 Further Comments

10 Example

10.1 Program Text

10.2 Program Data

10.3 Program Results

NAG CL Interface
s21cbc (jacellip_complex)