Note

This is the documentation for the current state of the development branch of Qiskit Experiments. The documentation or APIs here can change prior to being released.

frequency

frequency(x, y, filter_window=5, filter_dim=2)[source]

Get frequency of oscillating signal.

First this tries FFT. If the true value is likely below or near the frequency resolution, the function tries low frequency fit with

\[f_{\rm est} = \frac{1}{2\pi {\rm max}\left| y \right|} {\rm max} \left| \frac{dy}{dx} \right|\]

given \(y = A \cos (2\pi f x + phi)\). In this mode, y data points are smoothed by a Savitzky-Golay filter to protect against outlier points.

Note

This function returns always positive frequency. This function is sensitive to the DC offset. This function assumes sorted, no-overlapping x values.

Parameters:

  • x (ndarray) – Array of x values.

  • y (ndarray) – Array of y values.

  • filter_window (int) – Window size of Savitzky-Golay filter. This should be odd number.

  • filter_dim (int) – Dimension of Savitzky-Golay filter.

Returns:

Frequency estimation of oscillation signal.

Return type:

float