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

NAME

vdfftb - compute a periodic sequence from its Fourier coefficients. 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/output)
  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 specified in a dimension or type statement. MDIMX > = M.

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