clouddrift.wavelet.morse_freq

clouddrift.wavelet.morse_freq(gamma: ndarray | float, beta: ndarray | float) → tuple[ndarray] | tuple[float]

Frequency measures for generalized Morse wavelets. This functions calculates three different measures fm, fe, and fi of the frequency of the lowest-order generalized Morse wavelet specified by parameters gamma and beta.

Note that all frequency quantities here are in radian as in cos(f t) and not cyclic as in np.cos(2 np.pi f t).

For beta=0, the corresponding wavelet becomes an analytic lowpass filter, and fm is not defined in the usual way but as the point at which the filter has decayed to one-half of its peak power.

For details see Lilly and Olhede (2009), doi: 10.1109/TSP.2008.2007607.

Parameters

gammanp.ndarray or float

Gamma parameter of the wavelets.

betanp.ndarray or float

Beta parameter of the wavelets.

Returns

fmnp.ndarray

The modal or peak frequency.

fenp.ndarray

The energy frequency.

finp.ndarray

The instantaneous frequency at the wavelets’ centers.

Examples

>>> fm, fe, fi = morse_freq(3, 4)

>>> morse_freq(3, 4)
(array(1.10064242), 1.1025129235952809, 1.1077321674324723)

>>> morse_freq(3, np.array([10, 20, 30]))
(array([1.49380158, 1.88207206, 2.15443469]),
array([1.49421505, 1.88220264, 2.15450116]),
array([1.49543843, 1.88259299, 2.15470024]))

>>> morse_freq(np.array([3, 4, 5]), np.array([10, 20, 30]))
(array([1.49380158, 1.49534878, 1.43096908]),
array([1.49421505, 1.49080278, 1.4262489 ]),
array([1.49543843, 1.48652036, 1.42163583]))

>>> morse_freq(np.array([3, 4, 5]), 10)
(array([1.49380158, 1.25743343, 1.14869835]),
array([1.49421505, 1.25000964, 1.13759731]),
array([1.49543843, 1.24350315, 1.12739747]))

See Also

morse_wavelet(), morse_amplitude()