SYNOPSIS
CALL FFT99 ( a,work,trigs,ifax,inc,jump,n,m,isign )
CALL FFT991 ( a,work,trigs,ifax,inc,jump,n,m,isign )
DESCRIPTION
a - real variable of dimension (n+2)
This array contains the input data or coefficient vectors.
This array is overwritten by the results.
work - real variable of dimension ( min0(m,64)*(n+1) )
trigs - real variable of dimension (n)
ifax - integer varable of dimension (10)
Trigs and ifax are created by the subroutine SET99.
inc - the word increment between successive elements of each data
or coefficient vector e.g. inc=1 for consecutively stored data.
jump - the word increment between the first elements of successive
data or coefficient vectors
n - the length of each transform. n has prime factors of 2,3,5 only
(n may be odd)
m - the number of transforms to be done simultaneously
isign - specify sense of fft calculation.
+1 for a transform from fourier
coefficients to data values.
-1 for a transform from data values
to fourier coefficients
a contains either the coefficients or the data values, depending
on ISIGN. In each case n independent quantities occupy n+2 words.
The coefficients are stored as successive pairs of real and
imaginary parts - A(K),B(K) , K=0,1,...n/2
B(0) and B(n/2) are stored although they must be 0.
For FFT99 the data is stored with explicit periodicity -
X(n-1),X(0),X(1),....X(n-1),X(0)
ECMWF 1 ECMWF
FFT99(3) Local ECMWF Utility FFT99(3)
calling FFT99 or FFT991.
FILES
/usr/local/lib/eclib.a
REFERENCES
Author : C. Temperton.
Specialist : C. Temperton.
ECMWF Technical Report no.3
ECMWF Internal Report no.21
Very Fast Real Fourier Transforms in Special Topics of Applied
Mathematics - C. Temperton.