Contents

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

NAME

     dfftb - compute a periodic sequence from its Fourier coeffi-
     cients.   The DFFT operations are unnormalized, so a call of
     DFFTF followed by a call of DFFTB will  multiply  the  input
     sequence by N.

SYNOPSIS

     SUBROUTINE DFFTB(N, X, WSAVE)

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

     SUBROUTINE DFFTB_64(N, X, WSAVE)

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

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

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

     SUBROUTINE FFTB_64([N], X, WSAVE)

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

  C INTERFACE
     #include <sunperf.h>

     void dfftb(int n, double *x, double *wsave);

     void dfftb_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.