nag_prob_landau (g01etc) (PDF version)
g01 Chapter Contents
g01 Chapter Introduction
NAG Library Manual

NAG Library Function Document

nag_prob_landau (g01etc)

+− 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

1  Purpose

nag_prob_landau (g01etc) returns the value of the Landau distribution function Φλ.

2  Specification

#include <nag.h>
#include <nagg01.h>
double  nag_prob_landau (double x)

3  Description

nag_prob_landau (g01etc) evaluates an approximation to the Landau distribution function Φλ given by
Φλ=∫-∞λϕλdλ,
where ϕλ is described in nag_prob_density_landau (g01mtc), using piecewise approximation by rational functions. Further details can be found in Kölbig and Schorr (1984).

4  References

Kölbig K S and Schorr B (1984) A program package for the Landau distribution Comp. Phys. Comm. 31 97–111

5  Arguments

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

6  Error Indicators and Warnings

None.

7  Accuracy

At least 7 significant digits are usually correct, but occasionally only 6. Such accuracy is normally considered to be adequate for applications in experimental physics.
Because of the asymptotic behaviour of Φλ, which is of the order of exp-exp-λ, underflow may occur on some machines when λ is moderately large and negative.

8  Parallelism and Performance

Not applicable.

9  Further Comments

None.

10  Example

This example evaluates Φλ at λ=0.5, and prints the results.

10.1  Program Text

Program Text (g01etce.c)

10.2  Program Data

Program Data (g01etce.d)

10.3  Program Results

Program Results (g01etce.r)

nag_prob_landau (g01etc) (PDF version)
g01 Chapter Contents
g01 Chapter Introduction
NAG Library Manual
© The Numerical Algorithms Group Ltd, Oxford, UK. 2014