Inverse fast Fourier transform

Syntax: | `y = IFFT(m) y = IFFT(m,'AMP&PHASE') y = IFFT(m,'COS&SIN')`

The `IFFT` function calculates the inverse discrete Fourier transform of the two column input matrix. This matrix is usually calculated by the `FFT` function, thus reconstructing the original data.

By default, `IFFT` expects amplitudes and phases, where the phases are in degrees. The first column of the matrix should contain the amplitudes and the second column the phases. If the `COS&SIN` keyword is used, `IFFT` expects the Fourier coefficients, that is, the cosine coefficients in the first column and the sine coefficients in the second column. If the input matrix has `N` rows, the function returns a vector with length `2(N-1)`.

The principle usage of the `IFFT` function is to modify some of the amplitudes returned from the `FFT` function and note their effect on the original data. A typical application would be one of data smoothing, in which the user would zero out the amplitudes of the higher order harmonics.