Contents
dfftf - compute the Fourier coefficients of a periodic
sequence. The FFT operations are unnormalized, so a call of
DFFTF followed by a call of DFFTB will multiply the input
sequence by N.
SUBROUTINE DFFTF(N, X, WSAVE)
INTEGER N
DOUBLE PRECISION X(*), WSAVE(*)
SUBROUTINE DFFTF_64(N, X, WSAVE)
INTEGER*8 N
DOUBLE PRECISION X(*), WSAVE(*)
F95 INTERFACE
SUBROUTINE FFTF([N], X, WSAVE)
INTEGER :: N
REAL(8), DIMENSION(:) :: X, WSAVE
SUBROUTINE FFTF_64([N], X, WSAVE)
INTEGER(8) :: N
REAL(8), DIMENSION(:) :: X, WSAVE
C INTERFACE
#include <sunperf.h>
void dfftf(int n, double *x, double *wsave);
void dfftf_64(long n, double *x, double *wsave);
N (input) Length of the sequence to be transformed. These
subroutines are most efficient when N is a product
of small primes. N >= 0.
X (input) On entry, an array of length N containing the
sequence to be transformed.
WSAVE (input)
On entry, WSAVE must be an array of dimension (2 *
N + 15) or greater and must have been initialized
by DFFTI.