G01ETF (PDF version)
G01 Chapter Contents
G01 Chapter Introduction
NAG Library Manual
NAG Library Routine Document
G01ETF
Note:
before using this routine, please read the Users' Note for your implementation to check the interpretation of
bold italicised
terms and other implementation-dependent details.
▸
▿
Contents
1
Purpose
2
Specification
3
Description
4
References
5
Parameters
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
G01ETF returns the value of the Landau distribution function
Φ
λ
, via the routine name.
2 Specification
FUNCTION G01ETF (
X
)
REAL (KIND=nag_wp) G01ETF
REAL (KIND=nag_wp)
X
3 Description
G01ETF evaluates an approximation to the Landau distribution function
Φ
λ
given by
Φ
λ
=
∫
-
∞
λ
ϕ
λ
d
λ
,
where
ϕ
λ
is described in
G01MTF
, 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 Parameters
1:
X
– REAL (KIND=nag_wp)
Input
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
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
Not applicable.
9 Further Comments
None.
10 Example
This example evaluates
Φ
λ
at
λ
=
0.5
, and prints the results.
10.1 Program Text
Program Text (g01etfe.f90)
10.2 Program Data
Program Data (g01etfe.d)
10.3 Program Results
Program Results (g01etfe.r)
G01ETF (PDF version)
G01 Chapter Contents
G01 Chapter Introduction
NAG Library Manual
© The Numerical Algorithms Group Ltd, Oxford, UK. 2015