# sgrid

draws a s-plane grid

### Syntax

sgrid() sgrid(zeta, wn) sgrid(.., colors) sgrid(.., "new")

### Arguments

- zeta
vector of damping factors. Only values in

`[0 1]`

are taken into account. The default values are ~ cosd(90:-10:0) =`[0 0.17 0.34 0.5 0.64 0.77 0.87 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 a vector with 2 elements [circles_col, rays_col], specifying the color(s) of circles and rays of the frame, and their labels: predefined colors names (like "red"), or colors hexadecimal codes (like "#34DDFA"), or colors indices in the current colormap are accepted.

- "new"
This option clears all contents of the current axes before plotting the grid. It may be specified at any position among input arguments.

### Description

The `sgrid`

function is often used to draw a grid
for Evans 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.

`sgrid`

plots curves of constant damping ratio at values given
by `zeta`

, and constant natural frequency at values 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)`

).

`sgrid(), sgrid("new"), sgrid(colors)`

or
`sgrid(colors, "new")`

plots a default grid.

### Examples

Post-tuning graphical elements of the grid:

sgrid() sGrid = gca().children.children.children; i = find(sGrid(3:$).type=="Polyline" & sGrid(1:$-2).type=="Polyline",1); Circles = sGrid(1:i-1); Circ_text = Circles(Circles.type=="Text"); // Labels Circ_text.font_size = 2; Circ_lines = Circles(Circles.type=="Polyline"); // Circles Circ_lines.line_style = 8; Rays = sGrid(i:$); Rays(Rays.type=="Text").font_foreground = color("light slate blue"); Rays_lines = Rays(Rays.type=="Polyline"); set(Rays_lines, "line_style", 9, "thickness", 1.5);

Evans plot + a s grid:

### See also

- evans — Evans root locus
- zgrid — zgrid plot
- hallchart — Draws the Hall chart
- nicholschart — Nichols chart

### History

Version | Description |

6.0.2 | colors can be specified by their names or by their #RRGGBB code |

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