Contents

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

NAME

     vdfftb - compute a periodic sequence from its Fourier  coef-
     ficients.  The VRFFT operations are normalized, so a call of
     VRFFTF followed by a call of VRFFTB will return the original
     sequence.

SYNOPSIS

     SUBROUTINE VDFFTB(M, N, X, XT, MDIMX, WSAVE)

     INTEGER M, N, MDIMX
     DOUBLE PRECISION X(MDIMX,*), XT(MDIMX,*), WSAVE(*)

     SUBROUTINE VDFFTB_64(M, N, X, XT, MDIMX, WSAVE)

     INTEGER*8 M, N, MDIMX
     DOUBLE PRECISION X(MDIMX,*), XT(MDIMX,*), WSAVE(*)

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

     INTEGER :: M, N, MDIMX
     REAL(8), DIMENSION(:) :: WSAVE
     REAL(8), DIMENSION(:,:) :: X, XT

     SUBROUTINE FFTB_64([M], [N], X, XT, [MDIMX], WSAVE)

     INTEGER(8) :: M, N, MDIMX
     REAL(8), DIMENSION(:) :: WSAVE
     REAL(8), DIMENSION(:,:) :: X, XT

  C INTERFACE
     #include <sunperf.h>

     void vdfftb(int m, int n, double *x, double *xt, int  mdimx,
               double *wsave);

     void vdfftb_64(long m, long n, double *x, double  *xt,  long
               mdimx, double *wsave);

ARGUMENTS

     M (input) The number of sequences to be transformed.   M  >=
               0.

     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.  For VRFFTF, a real
               two-dimensional array X(M,N)  whose  rows  contain
               the sequences to be transformed.

     XT (input)
               A real two-dimensional work array with  dimensions
               of (MDIMX x N).

     MDIMX (input)
               Leading dimension of the arrays X and XT as speci-
               fied  in  a dimension or type statement.  MDIMX >=
               M.

     WSAVE (input)
               On entry, an array of dimension (N+15) or  greater
               initialized by VRFFTI.