EZFFTF(3)

SYNOPSIS
SUBROUTINE EZFFTF (N, R, AZERO, A, B, WSAVE)

NAME
ezfftf - Compute a simplified real, periodic, fast Fourier forward transform.

LIBRARY
SLATEC (FFTPACK)

CATEGORY
J1A1

TYPE
SINGLE PRECISION (EZFFTF-S)

KEYWORDS
FFTPACK, FOURIER TRANSFORM

AUTHOR
Swarztrauber, P. N., (NCAR)

DESCRIPTION
Subroutine EZFFTF computes the Fourier coefficients of a real periodic sequence (Fourier analysis). The transform is defined below at Output Parameters AZERO, A and B. EZFFTF is a simplified but slower version of RFFTF. Input Parameters N the length of the array R to be transformed. The method is most efficient when N is the product of small primes. R a real array of length N which contains the sequence to be transformed. R is not destroyed. WSAVE a work array which must be dimensioned at least 3*N+15 in the program that calls EZFFTF. The WSAVE array must be initialized by calling subroutine EZFFTI(N,WSAVE), and a different WSAVE array must be used for each different value of N. This initialization does not have to be repeated so long as N remains unchanged. Thus subsequent transforms can be obtained faster than the first. The same WSAVE array can be used by EZFFTF and EZFFTB. Output Parameters AZERO the sum from I=1 to I=N of R(I)/N A,B for N even B(N/2)=0. and A(N/2) is the sum from I=1 to I=N of (-1)**(I-1)*R(I)/N for N even define KMAX=N/2-1 for N odd define KMAX=(N-1)/2 then for K=1,...,KMAX A(K) equals the sum from I=1 to I=N of 2./N*R(I)*COS(K*(I-1)*2*PI/N) B(K) equals the sum from I=1 to I=N of 2./N*R(I)*SIN(K*(I-1)*2*PI/N)

REFERENCES
P. N. Swarztrauber, Vectorizing the FFTs, in Parallel Computations (G. Rodrigue, ed.), Academic Press, 1982, pp. 51-83.

ROUTINES CALLED
RFFTF

REVISION HISTORY (YYMMDD)
790601 DATE WRITTEN
830401 Modified to use SLATEC library source file format.
860115 Modified by Ron Boisvert to adhere to Fortran 77 by (a) changing dummy array size declarations (1) to (*), (b) changing references to intrinsic function FLOAT to REAL.
881128 Modified by Dick Valent to meet prologue standards.
890531 Changed all specific intrinsics to generic. (WRB)
890531 REVISION DATE from Version 3.2
891214 Prologue converted to Version 4.0 format. (BAB)
920501 Reformatted the REFERENCES section. (WRB)