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

NAME

vcfftb - compute a periodic sequence from its Fourier coefficients. The VCFFT operations are normalized, so a call of VCFFTF followed by a call of VCFFTB will return the original sequence.

SYNOPSIS

  SUBROUTINE VCFFTB( M, N, X, XT, MDIMX, ROWCOL, WSAVE)
  CHARACTER * 1 ROWCOL
  COMPLEX X(MDIMX,*), XT(MDIMX,*), WSAVE(*)
  INTEGER M, N, MDIMX

  SUBROUTINE VCFFTB_64( M, N, X, XT, MDIMX, ROWCOL, WSAVE)
  CHARACTER * 1 ROWCOL
  COMPLEX X(MDIMX,*), XT(MDIMX,*), WSAVE(*)
  INTEGER*8 M, N, MDIMX

F95 INTERFACE

  SUBROUTINE FFTB( [M], [N], X, XT, [MDIMX], ROWCOL, WSAVE)
  CHARACTER(LEN=1) :: ROWCOL
  COMPLEX, DIMENSION(:) :: WSAVE
  COMPLEX, DIMENSION(:,:) :: X, XT
  INTEGER :: M, N, MDIMX

  SUBROUTINE FFTB_64( [M], [N], X, XT, [MDIMX], ROWCOL, WSAVE)
  CHARACTER(LEN=1) :: ROWCOL
  COMPLEX, DIMENSION(:) :: WSAVE
  COMPLEX, DIMENSION(:,:) :: X, XT
  INTEGER(8) :: M, N, MDIMX

C INTERFACE

#include <sunperf.h>

void vcfftb(int m, int n, complex *x, complex *xt, int mdimx, char rowcol, complex *wsave);

void vcfftb_64(long m, long n, complex *x, complex *xt, long mdimx, char rowcol, complex *wsave);

ARGUMENTS

• M (input)
  If ROWCOL = 'R' or 'r', M is the number of sequences to be transformed. Otherwise, M is the length of the sequences to be transformed. M > = 0.

• N (input)
  If ROWCOL = 'R' or 'r', N is the length of the sequences to be transformed. Otherwise, N is the number of sequences to be transformed. N > = 0.

• X (input/output)
  On entry, if ROWCOL = 'R' or 'r' X(MDIMX,N) is an array whose first M rows contain the sequences to be transformed. Otherwise, X(MDIMX,N) contains data sequences of length M stored in N columns of X.

• XT (input)
  A work array. The size of this workspace depends on the number of threads that are used to execute this routine. There are various functions that can be used to determine the number of threads available (get_env, available_threads, etc). The appropriate amount, which is (number of threads * length of data sequences), can then be dynamically allocated for XT from the driver routine. If XT can only be allocated statically, then the size of XT should be (length of data sequences * number of sequences).

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

• ROWCOL (input)
  Indicates whether to transform rows ('R' or 'r') or columns ('C' or 'c').

• WSAVE (input)
  On entry, an array of dimension (L2+15) or greater, where L2 = 2*M if ROWCOL = ('R' or 'r'). Otherwise, L2 = 2*N. WSAVE is initialized by VCFFTI.