sgrid
=====

s-plane grid lines.



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


::

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




Arguments
~~~~~~~~~

:zeta array of damping factors. Only values in `[0 1]` are taken into
  account. The default value is `[0 0.16 0.34 0.5 0.64 0.76 0.86 0.94
  0.985 1]` .
: :wn array of natural frequencies in Hz. only positive values are
  taken into account. If not given it is computed by the program to fit
  with the boundaries of the plot.
: :colors a scalar or an 2 element array with integer values (color
  index).
:



Description
~~~~~~~~~~~

Plots selected curves of constant damping ratio (selection given by
`zeta`) and constant natural frequency (selection given by `wn`).

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

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

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



Examples
~~~~~~~~


::

    //sgrid
    `clf`_();sgrid(0:0.2:1,[0.2 0.6 1 1.7 2])





::

    H=`syslin`_('c',352*`poly`_(-5,'s')/`poly`_([0,0,2000,200,25,1],'s','c'));
    `clf`_();`evans`_(H,100);sgrid()






See Also
~~~~~~~~


+ `evans`_ Evans root locus
+ `zgrid`_ zgrid plot
+ `datatips`_ Tool for placing and editing tips along the plotted
  curves.


.. _evans: evans.html
.. _zgrid: zgrid.html
.. _datatips: datatips.html