NAG C Library Manual, Mark 26
NAG Library Manual, Mark 26
NAG AD Library Manual, Mark 26
s Chapter Contents
s Chapter Introduction

NAG C Library Function Document

nag_bessel_i1_scaled (s18cfc)

NAG C Library Manual, Mark 26
NAG Library Manual, Mark 26
NAG AD Library Manual, Mark 26
s Chapter Contents
s Chapter Introduction

▸▿ Contents

© The Numerical Algorithms Group Ltd. 2018

1
Purpose

nag_bessel_i1_scaled (s18cfc) returns a value of the scaled modified Bessel function e-xI1x.

2
Specification

#include <nag.h>
#include <nags.h>
double  nag_bessel_i1_scaled (double x)

3
Description

nag_bessel_i1_scaled (s18cfc) evaluates an approximation to e-xI1x, where I1 is a modified Bessel function of the first kind. The scaling factor e-x removes most of the variation in I1x.
The function uses the same Chebyshev expansions as nag_bessel_i1 (s18afc), which returns the unscaled value of I1x.

4
References

NIST Digital Library of Mathematical Functions

5
Arguments

1:     x – doubleInput
On entry: the argument x of the function.

6
Error Indicators and Warnings

None.

7
Accuracy

Relative errors in the argument are attenuated when propagated into the function value. When the accuracy of the argument is essentially limited by the machine precision, the accuracy of the function value will be similarly limited by at most a small multiple of the machine precision.

8
Parallelism and Performance

nag_bessel_i1_scaled (s18cfc) is not threaded in any implementation.

9
Further Comments

None.

10
Example

This example reads values of the argument x from a file, evaluates the function at each value of x and prints the results.

10.1
Program Text

Program Text (s18cfce.c)

10.2
Program Data

Program Data (s18cfce.d)

10.3
Program Results

Program Results (s18cfce.r)

NAG C Library Manual, Mark 26
NAG Library Manual, Mark 26
NAG AD Library Manual, Mark 26
s Chapter Contents
s Chapter Introduction
© The Numerical Algorithms Group Ltd. 2018