— Function File: [mag, phase, w] = nichols (sys, w, outputs, inputs)

Produce Nichols plot of a system.

Inputs

sys

System data structure (must be either purely continuous or discrete; see is_digital).

w

Frequency values for evaluation.

• if sys is continuous, then nichols evaluates G(jw).
• if sys is discrete, then nichols evaluates G(exp(jwT)), where T=sys. tsam is the system sampling time.
• the default frequency range is selected as follows (These steps are not performed if w is specified):
  1. via routine __bodquist__, isolate all poles and zeros away from w=0 (jw=0 or exp(jwT)=1) and select the frequency range based on the breakpoint locations of the frequencies.
  2. if sys is discrete time, the frequency range is limited to jwT in [0,2p*pi].
  3. A “smoothing” routine is used to ensure that the plot phase does not change excessively from point to point and that singular points (e.g., crossovers from +/- 180) are accurately shown.

outputs

inputs

the names or indices of the output(s) and input(s) to be used in the frequency response; see sysprune.

Outputs

mag

phase

The magnitude and phase of the frequency response G(jw) or G(exp(jwT)) at the selected frequency values.

w

The vector of frequency values used.

If no output arguments are given, nichols plots the results to the screen. Descriptive labels are automatically placed. See xlabel, ylabel, and title.

Note: if the requested plot is for an MIMO system, mag is set to ||G(jw)|| or ||G(exp(jwT))|| and phase information is not computed.