Contents

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

NAME

     zfftb - compute a periodic sequence from its Fourier coeffi-
     cients.   The  FFT operations are unnormalized, so a call of
     ZFFTF followed by a call of ZFFTB will  multiply  the  input
     sequence by N.

SYNOPSIS

     SUBROUTINE ZFFTB(N, X, WSAVE)

     DOUBLE COMPLEX X(*)
     INTEGER N
     DOUBLE PRECISION WSAVE(*)

     SUBROUTINE ZFFTB_64(N, X, WSAVE)

     DOUBLE COMPLEX X(*)
     INTEGER*8 N
     DOUBLE PRECISION WSAVE(*)

  F95 INTERFACE
     SUBROUTINE FFTB([N], X, WSAVE)

     COMPLEX(8), DIMENSION(:) :: X
     INTEGER :: N
     REAL(8), DIMENSION(:) :: WSAVE

     SUBROUTINE FFTB_64([N], X, WSAVE)

     COMPLEX(8), DIMENSION(:) :: X
     INTEGER(8) :: N
     REAL(8), DIMENSION(:) :: WSAVE

  C INTERFACE
     #include <sunperf.h>

     void zfftb(int n, doublecomplex *x, double *wsave);

     void zfftb_64(long n, doublecomplex *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/output)
               On entry, WSAVE must be an array of dimension (4 *
               N  + 15) or greater and must have been initialized
               by ZFFTI.