kontrol.transfer_function

Primary modules

kontrol.transfer_function.transfer_function

Transfer function class. Wrapper around control.TransferFunction to provide custom functionality related to KAGRA.

class kontrol.transfer_function.transfer_function.TransferFunction(*args)

Bases: TransferFunction

Transfer function class

Parameters

*args – Arguments passed to control.TransferFunction class.

clean(tol_order=5)

Remove numerator/denominator coefficients that are small outliers

Parameters

tol_order (int, optional) – If the coefficient is tol_order order smaller than the rest of the coefficients, then this coefficient is an outlier. Defaults 5.

foton(expression='zpk', root_location='s', significant_figures=6, itol=1e-25, epsilon=1e-25)

Foton expression of this transfer function

Calls kontrol.core.foton.tf2foton and returns a foton expression of this transfer function

Parameters

  • expression (str, optional) – Format of the foton expression. Choose from [“zpk”, “rpoly”]. Defaults to “zpk”.

  • root_location (str, optional) – Root location of the zeros and poles for expression==”zpk”. Choose from [“s”, “f”, “n”]. “s”: roots in s-plane, i.e. zpk([…], […], …, “s”). “f”: roots in frequency plane, i.e. zpk([…], [,,,], …, “f”). “n”: roots in frequency plane but negated and gains are normalized, i.e. real parts are positive zpk([…], […], …, “n”). Defaults to “s”.

  • significant_figures (int, optional) – Number of significant figures to print out. Defaults to 6.

  • itol (float, optional) – Treating complex roots as real roots if the ratio of the imaginary part and the real part is smaller than this tolerance Defaults to 1e-25.

  • epsilon (float, optional) – Small number to add to denominator to prevent division error. Defaults to 1e-25.

Returns

foton_expression – The foton expression in selected format.

Return type

str

lstrip(element, fc=None)

Remove zero or pole from the left.

Parameters

  • element (str) – Element to be removed. Choose from [“any”, “zero”, “pole”, “pair”, “all”].

  • fc (float or None, optional) – Cutoff frequency. If element is in [“any”, “all”], remove any or all elements on the left of the cutoff. Defaults None.

rstrip(element, fc=None)

Remove zero or pole from the right.

Parameters

  • element (str) – Element to be removed. Choose from [“any”, “zero”, “pole”, “pair”, “all”].

  • fc (float or None, optional) – Cutoff frequency. If element is in [“any”, “all”], remove any or all elements on the left of the cutoff. Defaults None.

save(path, overwrite=True)

Save the transfer function to a specified path.

This functions extracts the numerator and denominator coefficients and puts it into a pandas DataFrame with keys {“num” and “den”}. Then it outputs to the specified path with a pickle format.

Parameters

  • path (str) – The string of the path.

  • overwrite (boolean, optional) – Overwrite if the file exists.

stabilize()

Convert unstable zeros and poles to stable ones.

kontrol.transfer_function.transfer_function.load_transfer_function(path)

Load a kontrol TransferFunction object from path.

Parameters

path (str) – The path of the saved transfer function

Returns

The loaded TransferFunction object.

Return type

TransferFunction

kontrol.transfer_function.notch

Foton defined Notch filter.

class kontrol.transfer_function.notch.Notch(frequency, q, depth=None, depth_db=None)

Bases: TransferFunction

Notch Filter Object

Parameters

  • frequency (float) – The notch frequency (Hz).

  • q (float) – The quality factor.

  • depth (float) – The depth of the notch filter (magnitude). If not specified, depth_db will be used. Defaults None.

  • depth_db (float, optional) – The depth of the notch filter (decibel). If not specified, depth will be used instead. Defaults None.

  • Attritubes –

  • ---------- –

  • frequency – The notch frequency (Hz).

  • q – The quality factor.

  • depth – The depth of the notch filter (magnitude).

Notes

The notch filter is defined by Foton, as

\[N(s) = \frac{s^2 + (2\pi f_n)/(dQ/2)s + (2\pi f_n)^2} {s^2 + (2\pi f_n)/(Q/2)s + (2\pi f_n)^2}\,,\]

where \(f_n\) is the notch frequency, \(q\) is the quality factor , and \(d\) is the depth.

property depth

The depth of the notch filter (magnitude).

foton()

Foton expression of this notch filter.

property frequency

The notch frequency (Hz).

property q

The quality factor