class control.FRD(*args, **kwargs)

A class for models defined by Frequency Response Data (FRD)

The FRD class is used to represent systems in frequency response data form.

The main data members are ‘omega’ and ‘fresp’, where omega is a 1D array with the frequency points of the response, and fresp is a 3D array, with the first dimension corresponding to the output index of the FRD, the second dimension corresponding to the input index, and the 3rd dimension corresponding to the frequency points in omega. For example,

>>> frdata[2,5,:] = numpy.array([1., 0.8-0.2j, 0.2-0.8j])

means that the frequency response from the 6th input to the 3rd output at the frequencies defined in omega is set to the array above, i.e. the rows represent the outputs and the columns represent the inputs.

__init__(*args, **kwargs)

Construct an FRD object

The default constructor is FRD(d, w), where w is an iterable of frequency points, and d is the matching frequency data.

If d is a single list, 1d array, or tuple, a SISO system description is assumed. d can also be

To call the copy constructor, call FRD(sys), where sys is a FRD object.

To construct frequency response data for an existing LTI object, other than an FRD, call FRD(sys, omega)


Return the zero-frequency gain


Evaluate a transfer function at a single angular frequency.

self.evalfr(omega) returns the value of the frequency response at frequency omega.

Note that a “normal” FRD only returns values for which there is an entry in the omega vector. An interpolating FRD can return intermediate values.

feedback(other=1, sign=-1)

Feedback interconnection between two FRD objects.


Evaluate a transfer function at a list of angular frequencies.

mag, phase, omega = self.freqresp(omega)

reports the value of the magnitude, phase, and angular frequency of the transfer function matrix evaluated at s = i * omega, where omega is a list of angular frequencies, and is a sorted version of the input omega.


Check to see if a system is a continuous-time system


sys : LTI system

System to be checked

strict: bool (default = False) :

If strict is True, make sure that timebase is not None


Check to see if a system is a discrete-time system


strict: bool (default = False) :

If strict is True, make sure that timebase is not None