FFTW - Inverse FFT input data

1. How do you do inverse FFT?
2. How do you convert FFT to ifft?
3. What does FFTW really compute?
4. Is FFTW free?

How do you do inverse FFT?

X = ifft( Y ) computes the inverse discrete Fourier transform of Y using a fast Fourier transform algorithm. X is the same size as Y . If Y is a vector, then ifft(Y) returns the inverse transform of the vector. If Y is a matrix, then ifft(Y) returns the inverse transform of each column of the matrix.

How do you convert FFT to ifft?

A quick and easy way to get an IFFT if you only have an FFT is to do conjugate -> FFT -> conjugate -> scale (optional) . Most cell phones only have 1 FFT chip, and the reason being that chip can do FFT and IFFT. To obtain the IFFT you need to do the FFT, scale the result, and shift the result.

What does FFTW really compute?

FFTW computes an unnormalized transform, that is, the equation IFFT(FFT(X)) = n X holds. In other words, applying the forward and then the backward transform will multiply the input by n. An FFTW_FORWARD transform corresponds to a sign of -1 in the exponent of the DFT.

Is FFTW free?

We believe that FFTW, which is free software, should become the FFT library of choice for most applications. The latest official release of FFTW is version 3.3. 10, available from our download page.