@@ -44,7 +44,43 @@ def __init__(self, inputs=1, outputs=1, states=None, name=None, **kwargs):
4444def __call__ (self ,x ,squeeze = None ,warn_infinite = True ):
4545"""Evaluate system transfer function at point in complex plane.
4646
47- See `StateSpace.__call__` and `TransferFunction.__call__` for details.
47+ Returns the value of the system's transfer function at a point `x`
48+ in the complex plane, where `x` is `s` for continuous-time systems
49+ and `z` for discrete-time systems.
50+
51+ By default, a (complex) scalar will be returned for SISO systems
52+ and a p x m array will be return for MIMO systems with m inputs and
53+ p outputs. This can be changed using the `squeeze` keyword.
54+
55+ To evaluate at a frequency `omega` in radians per second,
56+ enter ``x = omega * 1j`` for continuous-time systems,
57+ ``x = exp(1j * omega * dt)`` for discrete-time systems, or
58+ use the `~LTI.frequency_response` method.
59+
60+ Parameters
61+ ----------
62+ x : complex or complex 1D array_like
63+ Complex value(s) at which transfer function will be evaluated.
64+ squeeze : bool, optional
65+ Squeeze output, as described below. Default value can be set
66+ using `config.defaults['control.squeeze_frequency_response']`.
67+ warn_infinite : bool, optional
68+ If set to False, turn off divide by zero warning.
69+
70+ Returns
71+ -------
72+ fresp : complex ndarray
73+ The value of the system transfer function at `x`. If the system
74+ is SISO and `squeeze` is not True, the shape of the array matches
75+ the shape of `x`. If the system is not SISO or `squeeze` is
76+ False, the first two dimensions of the array are indices for the
77+ output and input and the remaining dimensions match `x`. If
78+ `squeeze` is True then single-dimensional axes are removed.
79+
80+ Notes
81+ -----
82+ See `FrequencyResponseData`.__call__`, `StateSpace.__call__`,
83+ `TransferFunction.__call__` for class-specific details.
4884
4985 """
5086raise NotImplementedError ("not implemented in subclass" )
@@ -117,7 +153,7 @@ def frequency_response(self, omega=None, squeeze=None):
117153
118154def dcgain (self ):
119155"""Return the zero-frequency (DC) gain."""
120- return NotImplemented
156+ raise NotImplementedError ( "dcgain not defined for subclass" )
121157
122158def _dcgain (self ,warn_infinite ):
123159zeroresp = self (0 if self .isctime ()else 1 ,
@@ -443,8 +479,7 @@ def evalfr(sys, x, squeeze=None):
443479
444480 See Also
445481 --------
446- StateSpace.__call__, TransferFunction.__call__, frequency_response,\
447-
482+ LTI.__call__, frequency_response, bode_plot
448483
449484 Notes
450485 -----