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NAME
     vdfftb - compute a periodic sequence from its Fourier  coef-
     ficients.   The  xFFT operations are unnormalized, so a call
     of xFFTF followed by a call of xFFTB will multiply the input
     sequence  by  N.   The VxFFT operations are normalized, so a
     call of VxFFTF followed by a call of VxFFTB will return  the
     original sequence.

SYNOPSIS
     SUBROUTINE RFFTB (N, RX, RWSAVE)

     SUBROUTINE DFFTB (N, DX, DWSAVE)

     SUBROUTINE CFFTB (N, RX, RWSAVE)

     SUBROUTINE ZFFTB (N, DX, DWSAVE)

     SUBROUTINE VRFFTB (M, N, RX, RXT, MDIMX, RWSAVE)

     SUBROUTINE VDFFTB (M, N, DX, DXT, MDIMX, DWSAVE)



     #include <sunperf.h>

     void rfftb (int n, float *r, float *wsave) ;

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

     void cfftb (int n, complex *cc, complex *wsave) ;

     void zfftb (int n, doublecomplex *zc, doublecomplex  *wsave)
               ;

     void vrfftb(int m, int n, float *r, int mdimr, float *wsave)
               ;

     void vdfftb(int m, int  n,  double  *r,  int  mdimr,  double
               *wsave) ;

ARGUMENTS
     M         (For vector operations only.)
               The number of sequences to be transformed.   M  >=
               0.

     N         Length of the sequence to be  transformed.   These
               subroutines are most efficient when N is a product
               of small primes.  N >= 0.

     xX        On entry, an array  of  length  N  containing  the
               sequence  to  be  transformed.  For VxFFTF, a real
               two-dimensional array xX(M,N) whose  rows  contain
               the sequences to be transformed.

     xXT       (For vector operations only.)
               A real two-dimensional work array with  dimensions
               of (MDIMX x N).

     MDIMX     (For vector operations only.)
               Leading dimension of the  arrays  xX  and  xXT  as
               specified  in a dimension or type statement. MDIMX
               >= M.

     xWSAVE    On entry, an array with dimension for scalar  sub-
               routines  of at least (2 * N + 15) for real inputs
               or (4 * N + 15) for complex  inputs.   For  vector
               subroutines,  the  dimension  is  at least (N+15).
               The array must have been initialized by  xFFTI  or
               VxFFTI.

SAMPLE PROGRAM
           PROGRAM TEST
           IMPLICIT NONE
     C
           INTEGER           N
           PARAMETER        (N = 4)
     C
           INTEGER           I
           REAL              PI, WSAVE(4 * N + 15), X, Y
           COMPLEX           C(N)
     C
           EXTERNAL          CFFTB, CFFTF, CFFTI
           INTRINSIC         ACOS, CMPLX, COS, SIN
     C
     C     Initialize the array C to a complex sequence.
     C
           PI = ACOS (-1.0)
           DO 100, I=1, N
             X = SIN ((I - 1.0) * 2.0 * PI / N)
             Y = COS ((I - 1.0) * 2.0 * PI / N)
             C(I) = CMPLX (X, Y)
       100 CONTINUE
     C
           PRINT 1000
           PRINT 1010, (C(I), I = 1, N)
           CALL CFFTI (N, WSAVE)
           CALL CFFTF (N, C, WSAVE)
           PRINT 1020
           PRINT 1010, (C(I), I = 1, N)
           CALL CFFTB (N, C, WSAVE)
           PRINT 1030
           PRINT 1010, (C(I), I = 1, N)
     C
      1000 FORMAT (1X, 'Original Sequence:')
      1010 FORMAT (1X, 100(F4.1' +',F4.1,'i  '))
      1020 FORMAT (1X, 'Transformed Sequence:')
      1030 FORMAT (1X, 'Recovered Sequence:')
     C
           END

SAMPLE OUTPUT
      Original Sequence:
       0.0 + 1.0i   1.0 + 0.0i   0.0 +-1.0i  -1.0 + 0.0i
      Transformed Sequence:
       0.0 + 0.0i   0.0 + 0.0i   0.0 + 0.0i   0.0 + 4.0i
      Recovered Sequence:
       0.0 + 4.0i   4.0 + 0.0i   0.0 +-4.0i  -4.0 + 0.0i

Партнёры:

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