zgrid zgrid plot

## Syntax

                zgrid()
                zgrid(zeta, wn)
                zgrid('new', zeta, wn)
                zgrid(zeta, wn, 'new')
                zgrid(.., colors)

## Arguments

zeta

  array of damping factors. Only values in `[0 1]` are taken into account. The default value is `0:0.1:1`.

wn

  array of normalized natural frequencies (factors of π/dt). Only values in `[0 1]` are taken into account. The default value is `0:0.1:1`.

colors

  a scalar or an 2 element array with integer values (color index).

## Description

plots z-plane grid lines: lines of constant damping factor (selection given by `zeta`) and natural frequency (selection given by `wn`) are drawn in within the unit Z-plane circle.

Iso-frequency curves are shown in on the interval [0,%pi/dt].

The `colors` argument may be used to assign a color for constant damping ratio curves (`colors(2)`) and for frequency curves (`colors(1)`).

The `zgrid` function is often used to draw a grid for evens root locus of continuous time linear systems. In such a case the `zgrid` function should be called after the call to evans. For continuous time linear systems one should use sgrid function instead.

The optional argument `'new'` can be used to erase the graphic window before plotting the grid.

## Examples

        //zgrid
        clf();zgrid(0:0.2:1,[0.2 0.6 0.8 1])

zgrid(0:0.2:1,[0.2 0.6 0.8 1])

        //zgrid with discrete time system  root locus
        z=poly(0,'z')
        H=syslin(0.01,(0.54-1.8*z+2.9*z^2-2.6*z^3+z^4)/(0.8+0.78*z-0.1*z^2+0.9*z^3+z^4))
        clf();evans(H,1000);zgrid(0:0.1:0.5)

z=poly(0,'z') H=syslin(0.01,(0.54-1.8*z+2.9*z^2-2.6*z^3+z^4)/(0.8+0.78*z-0.1*z^2+0.9*z^3+z^4)) clf();evans(H,1000);zgrid(0:0.1:0.5)

## See also

- evans
- sgrid
- freson
- datatips