is too large, and the unscaled function is required, there is a risk of overflow and so no computation is performed. In all the above cases, a warning is given by the function.

4 References

NIST Digital Library of Mathematical Functions

Amos D E (1986) Algorithm 644: A portable package for Bessel functions of a complex argument and non-negative order ACM Trans. Math. Software 12 265–273

5 Arguments

1: $deriv$ – Nag_FunType Input

On entry: specifies whether the function or its derivative is required.

$deriv = Nag_Function$: $Ai (z)$ is returned.
$deriv = Nag_Deriv$: ${Ai}^{'} (z)$ is returned.

Constraint:

deriv = Nag_Function

Nag_Deriv

2: $z$ – Complex Input

On entry: the argument

z

of the function.

3: $scal$ – Nag_ScaleResType Input

On entry: the scaling option.

$scal = Nag_UnscaleRes$: The result is returned unscaled.
$scal = Nag_ScaleRes$: The result is returned scaled by the factor $e^{2 z \sqrt{z} / 3}$ .

Constraint:

scal = Nag_UnscaleRes

Nag_ScaleRes

4: $ai$ – Complex * Output

On exit: the required function or derivative value.

5: $nz$ – Integer * Output

On exit: indicates whether or not ai is set to zero due to underflow. This can only occur when

scal = Nag_UnscaleRes

$nz = 0$: ai is not set to zero.
$nz = 1$: ai is set to zero.

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_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_OVERFLOW_LIKELY: No computation because $ω . re$ too large, where $ω = (2 / 3) \times z^{(3 / 2)}$ .
NE_TERMINATION_FAILURE: No computation – algorithm termination condition not met.
NE_TOTAL_PRECISION_LOSS: No computation because $|z| = 〈value〉 > 〈value〉$ .
NW_SOME_PRECISION_LOSS: Results lack precision because $|z| = 〈value〉 > 〈value〉$ .

7 Accuracy

All constants in s17dgc are given to approximately

18

digits of precision. Calling the number of digits of precision in the floating-point arithmetic being used

t

, then clearly the maximum number of correct digits in the results obtained is limited by

p = \min (t, 18)

. Because of errors in argument reduction when computing elementary functions inside s17dgc, the actual number of correct digits is limited, in general, by

p - s

, where

s \approx \max (1, |\log_{10} |z||)

represents the number of digits lost due to the argument reduction. Thus the larger the value of

|z|

, the less the precision in the result.

Empirical tests with modest values of

z

, checking relations between Airy functions

Ai (z)

{Ai}^{'} (z)

Bi (z)

and

{Bi}^{'} (z)

, have shown errors limited to the least significant

3

–

4

digits of precision.

8 Parallelism and Performance

s17dgc is not threaded in any implementation.

9 Further Comments

Note that if the function is required to operate on a real argument only, then it may be much cheaper to call s17agc or s17ajc.

10 Example

This example prints a caption and then proceeds to read sets of data from the input data stream. The first datum is a value for the argument deriv, the second is a complex value for the argument, z, and the third is a character value used as a flag to set the argument scal. The program calls the function and prints the results. The process is repeated until the end of the input data stream is encountered.

Interfaces: FL CL AD

NAG CL Interface Introduction

S (Specfun) Chapter Contents

S (Specfun) Chapter Introduction

s17dg: FL CL AD

NAG CL Interfaces17dgc (airy_​ai_​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
s17dgc (airy_ai_complex)