nyquist

Syntax

nyquist(sys)

nyquist(sys, w)

nyquist(..., fmt, ...)

nyquist(..., property, value, ...)

[re, im, w] = nyquist(...)

Inputs

sys

A linear time-invariant transfer function or state space system.

Type: class

w

The vector of frequencies at which to compute the response. The units are radians/sec for continuous time, and Hz for discrete time. If w is a two-element vector, it contains the range of frequencies over which to compute the response. The units are radians/sec for continuous time, and Hz for discrete time.

Type: double

Dimension: vector

fmt

Plot format arguments. See the plot function help.

Type: string

Dimension: vector

property

Plot property arguments that are paired with a following value. See the plot function help.

Type: string

Dimension: vector

value

Plot property value arguments. See the plot function help.

Type: integer

Dimension: scalar

Outputs

re

The real component of the response.

Type: double

Dimension: vector

im

The imaginary component of the response.

Type: double

Dimension: vector

w

The vector of frequencies at which to compute the response. The units are radians/sec for continuous time, and Hz for discrete time.

Type: double

Dimension: vector

Example

Create the Nyquist diagram of the given 3rd order analog transfer function, with the plot in red.

tfo = tf([1,1,3,3],[1,-3,3,-1]);
nyquist(tfo,'r');

Figure 1. nyquist figure 1

Comments

If the output arguments are omitted, the function plots the results.

If w is omitted, then internally computed values are used.

By default, 500 points are plotted. More points can be requested using the w input, in which case it is typically best to specify them with logspace.

nyquist does not currently provide special treatment for sys inputs with poles or zeros on the imaginary axis.

nyquist does not currently support MIMO systems.