Contents

• NAME
• SYNOPSIS
  • F95 INTERFACE
  • C INTERFACE
• ARGUMENTS

NAME

     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.

SYNOPSIS

     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);

ARGUMENTS

     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.