NAG CL Interface
g01etc (prob_​landau)

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1 Purpose

g01etc returns the value of the Landau distribution function Φ(λ).

2 Specification

#include <nag.h>
double  g01etc (double x)
The function may be called by the names: g01etc, nag_stat_prob_landau or nag_prob_landau.

3 Description

g01etc evaluates an approximation to the Landau distribution function Φ(λ) given by
where ϕ(λ) is described in 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 double Input
On entry: the argument λ of the function.

6 Error Indicators and Warnings


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 Φ(λ), 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

Background information to multithreading can be found in the Multithreading documentation.
g01etc is not threaded in any implementation.

9 Further Comments


10 Example

This example evaluates Φ(λ) 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)