User`s guide

nichols
11-149
11nichols
Purpose Compute N ichols frequency response of LTI models
Syntax nichols(sys)
nichols(sys,w)
nichols(sys1,sys2,...,sysN)
nichols(sys1,sys2,...,sysN,w)
nichols(sys1,'PlotStyle1',...,sysN,'PlotStyleN')
[mag,phase,w] = nichols(sys)
[mag,phase] = nichols(sys,w)
Description nichols computes the frequency response of an LTI model and plots it in the
Nichols coordinates. Nichols plots are useful to analyze open- and closed-loop
properties of SISO systems, but offer little insight into MIMO control loops.
Use
ngrid to superimpose a Nichols chart on an existing SISO Nichols plot.
nichols(sys) produces a Nichols plot of the LTI model sys.Thismodelcanbe
continuous or discrete, SISO or MIMO. In the MIMO case,
nichols produces
an array of Nichols plots, each plot showing the response of one particular I/O
channel. The frequency range and gridding are d etermined automatically
based on the system poles and zeros.
nichols(sys,w) explicitly specifies the frequency range or frequency points to
be used for the plot. To focus on a particular frequency interval
[wmin,wmax],
set
w = {wmin,wmax}. To use particular frequency points, set w to the vector of
desired frequencies. Use
logspace to generate logarithmically spaced
frequency vectors. Frequencies should be specified in radians/sec.
nichols(sys1,sys2,...,sysN) or nichols(sys1,sys2,...,sysN,w)
superimpos es the Nichols plots of several LTI models on a single figure. All
systemsmust have the same number of inputs and outputs,but may otherwise
be a mix of continuous- and discrete-time systems. You can also specify a
distinctive color, linestyle, and/or marker for each system plot with the syntax
nichols(sys1,'PlotStyle1',...,sysN,'PlotStyleN')
See bode for an example.