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Improve center_frequency accuracy, fix edge case #575

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Improve center_frequency accuracy, fix edge case #575

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12 changes: 8 additions & 4 deletions pywt/_functions.py
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Original file line number Diff line number Diff line change
Expand Up @@ -153,11 +153,15 @@ def central_frequency(wavelet, precision=8):
domain = float(x[-1] - x[0])
assert domain > 0

index = np.argmax(abs(fft(psi)[1:])) + 2
if index > len(psi) / 2:
index = len(psi) - index + 2
# improve center frequency estimation by sampling DTFT(psi) more granularly
pad_factor = 3
psi_pad = np.pad(psi, [0, pad_factor * len(psi)])

return 1.0 / (domain / (index - 1))
index = np.argmax(abs(fft(psi_pad))[1:]) + 1 # omit dc, +1 to compensate
if index > len(psi_pad) / 2: # if negative freq, use index of positive
index = len(psi_pad) - index

return 1.0 / ((pad_factor + 1) * domain / index)


def scale2frequency(wavelet, scale, precision=8):
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