# ifft

## Purpose

Inverse 1-D fast Fourier transform.

## Synopsis

    y = ifft(x)
    y = ifft(x,n)

## Description

`ifft(x)` is the inverse fast Fourier transform of vector `x`.

`ifft(x,n)` is the `n`-point inverse FFT.

## Examples

For any `x`, `ifft(fft(x))` equals `x` to within roundoff error. If `x` is real, `ifft(fft(x))` may have small imaginary parts.

## Algorithm

The algorithm for `ifft(x)` is the same as the algorithm for `fft(x)`, except for a sign change and a scale factor of `n = length(x)`. So the execution time is fastest when `n` is a power of 2 and slowest when `n` is a large prime.

## See Also

    fft, fft2, fftshift, filter
    dftmtx, freqz, specplot, and spectrum in the Signal Processing Toolbox

(c) Copyright 1994 by The MathWorks, Inc.