zgrid
=====

zgrid plot



Calling Sequence
~~~~~~~~~~~~~~~~


::

    zgrid()
    zgrid(zeta,wn [,colors])
    zgrid(['new',] zeta,wn [,colors])
    zgrid(zeta,wn [,'new'] [,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 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)






See Also
~~~~~~~~


+ `evans`_ Evans root locus
+ `sgrid`_ s-plane grid lines.
+ `freson`_ peak frequencies
+ `datatips`_ Tool for placing and editing tips along the plotted
  curves.


.. _evans: evans.html
.. _freson: freson.html
.. _sgrid: sgrid.html
.. _datatips: datatips.html