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scipy.fft.

# rfftfreq

scipy.fft.rfftfreq(n, d=1.0, *, xp=None, device=None)

  Return the Discrete Fourier Transform sample frequencies (for usage with rfft, irfft).

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

  Unlike `fftfreq` (but like `scipy.fftpack.rfftfreq`) the Nyquist frequency component is considered to be positive.

  Parameters:
    nint

      Window length.

    dscalar, optional

      Sample spacing (inverse of the sampling rate). Defaults to 1.

    xparray_namespace, optional

      The namespace for the return array. Default is None, where NumPy is used.

    devicedevice, optional

      The device for the return array. Only valid when xp.fft.rfftfreq implements the device parameter.

  Returns:
    fndarray

      Array of length `n//2 + 1` containing the sample frequencies.

  Examples

      >>> import numpy as np
      >>> import scipy.fft
      >>> signal = np.array([-2, 8, 6, 4, 1, 0, 3, 5, -3, 4], dtype=float)
      >>> fourier = scipy.fft.rfft(signal)
      >>> n = signal.size
      >>> sample_rate = 100
      >>> freq = scipy.fft.fftfreq(n, d=1./sample_rate)
      >>> freq
      array([  0.,  10.,  20., ..., -30., -20., -10.])
      >>> freq = scipy.fft.rfftfreq(n, d=1./sample_rate)
      >>> freq
      array([  0.,  10.,  20.,  30.,  40.,  50.])