zfftb

NAME

zfftb - compute a periodic sequence from its Fourier coefficients. 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.