nlcpy.fft.fftfreq

nlcpy.fft.fftfreq(n, d=1.0)[source]

Returns the Discrete fourier transform sample frequencies.

The returned float array f contains the frequency bin centers in cycles per unit of the sample spacing (with zero at the start). For instance, if the sample spacing is in seconds, then the frequency unit is cycles/second. Given a window length n and a sample spacing d:

f = [0, 1, ...,   n/2-1,     -n/2, ..., -1] / (d*n)   if n is even
f = [0, 1, ..., (n-1)/2, -(n-1)/2, ..., -1] / (d*n)   if n is odd

Parameters

nint: Window length.
dscalar, optional: Sample spacing (inverse of the sampling rate). Defaults to 1.

Returns

fndarray: Array of length n containing the sample frequencies.

Examples

>>> import nlcpy as vp
>>> signal = vp.array([-2, 8, 6, 4, 1, 0, 3, 5], dtype=float)
>>> fourier = vp.fft.fft(signal)
>>> n = signal.size
>>> timestep = 0.1
>>> freq = vp.fft.fftfreq(n, d=timestep)
>>> freq
array([ 0.  ,  1.25,  2.5 ,  3.75, -5.  , -3.75, -2.5 , -1.25])