WRfft1b WRfft1f

WRfft1b() Function WRfft1b ( N As  Long, R As  Variant  ) One-dimensional real fast Fourier backward transforms Purpose WRfft1b 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. When N is even: R(K) = R(0) + (-1)^k R(N-1) + Σ(R(2*j-1)Cos(2*pi*j*k/N)) + Σ(R(2*j)Sin(2*pi*j*k/N)) (Σ for j = 1 to N/2-1) (k = 0 to N-1) When N is odd: R(K) = R(0) + Σ(R(2*j-1)Cos(2*pi*j*k/N)) + Σ(R(2*j)Sin(2*pi*j*k/N)) (Σ for j = 1 to (N-1)/2) (k = 0 to N-1) This transform is normalized since a call to WRfft1b followed by a call to WRfft1f (or vice-versa) reproduces the original array subject to algorithmic constraints, roundoff error, etc. Returns N x 1 Column 1 Rows 1 to N Fourier backward transformed data sequence 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] R (N) The sequence to be transformed. Reference FFTPACK Example See example of WRfft1f.