sgrid

sgrid — s-plane grid lines.

Calling sequence

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

Used in conjonction with evans, plots lines of constant damping ratio (zeta) and natural frequency (wn).

`sgrid()`	: add a grid over an existing continuous s-plane root with default values for `zeta` and `wn`.
`sgrid('new')`	: clears the graphic screen and then plots a default s-plane grid
`sgrid(zeta,wn [,color])`	: same as `sgrid()` but uses the provided damping ratio and natural frequency.



H=syslin('c',352*poly(-5,'s')/poly([0,0,2000,200,25,1],'s','c'));
evans(H,100)
sgrid()
sgrid(0.6,2,7)