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Zero-Pole Analysis

The zplane function plots poles and zeros of a linear system. For example, a simple filter with a zero at -1/2 and a complex pole pair at 0.9e–j2π(0.3) and 0.9ej2π(0.3) is

zer = -0.5; 
pol = 0.9*exp(j*2*pi*[-0.3 0.3]');

To view the pole-zero plot for this filter you can use

zplane(zer,pol)

or, for access to additional tools, use fvtool. First convert the poles and zeros to transfer function form, then call fvtool,

[b,a] = zp2tf(zer,pol,1);
fvtool(b,a)

and click the Pole/Zero Plot toolbar button on the toolbar or select Analysis > Pole/Zero Plot to see the plot.

For a system in zero-pole form, supply column vector arguments z and p to zplane:

zplane(z,p)

For a system in transfer function form, supply row vectors b and a as arguments to zplane:

zplane(b,a)

In this case zplane finds the roots of b and a using the roots function and plots the resulting zeros and poles.

See Linear System Models for details on zero-pole and transfer function representation of systems.

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