Cfft1b Cfft1f Cfft1i Cfftmb Cfftmf Cfftmi

Cfft1b() Sub Cfft1b ( N As  Long, C() As  Complex, Wsave() As  Double, Info As  Long, Optional Inc As  Long = 1  ) One-dimensional complex fast Fourier backward transform Purpose This routine computes the one-dimensional Fourier transform of a periodic sequence within a real array. This is referred to as the backward transform or Fourier synthesis, transforming the sequence from spectral to physical space. C(j) = ΣC(k)*exp(i*j*k*2π/N) (Σ for k = 0 to N-1) (j = 0 to N-1) (i is imaginary unit) This transform is normalized since a call to Cfft1b followed by a call to Cfft1f (or vice-versa) reproduces the original array subject to algorithmic constraints, roundoff error, etc. Parameters [in] N The length of the sequence to be transformed. (N >= 1) (The transform is most efficient when N is a product of small primes) [in,out] C() Array C(LC - 1) (LC >= Inc*(N - 1) + 1) [in] The sequence to be transformed. [out] The Fourier backward transformed sequence of data. [in] Wsave() Array Wsave(LWsave - 1) (LWsave >= 2*N + ln(N)/ln(2) + 4) Work data. Its contents must be initialized with a call to Cfft1i before the first call to Cfft1f or Cfft1b for a given transform length N. [out] Info = 0: Successful exit. = -1: The argument N had an illegal value. (N < 1) = -2: The argument C() is invalid. (Array C() is not big enough) = -3: The argument Wsave() is invalid. (Array Wsave() is not big enough) = -5: The argument Inc had an illegal value. (Inc < 1) [in] Inc (Optional) Integer increment between the locations, in array C(), of two consecutive elements within the sequence. (Inc >= 1) (default = 1) Reference FFTPACK Example Program See example of Cfft1f.