# Documentation

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# ngrid

Superimpose Nichols chart on Nichols plot

## Syntax

ngrid

## Description

ngrid  superimposes Nichols chart grid lines over the Nichols frequency response of a SISO LTI system. The range of the Nichols grid lines is set to encompass the entire Nichols frequency response.

The chart relates the complex number H/(1 + H) to H, where H is any complex number. For SISO systems, when H is a point on the open-loop frequency response, then

$\frac{H}{1+H}$

is the corresponding value of the closed-loop frequency response assuming unit negative feedback.

If the current axis is empty, ngrid generates a new Nichols chart grid in the region –40 dB to 40 dB in magnitude and –360 degrees to 0 degrees in phase. If the current axis does not contain a SISO Nichols frequency response, ngrid returns a warning.

## Examples

collapse all

Plot the Nichols response with Nichols grid lines for the following system:

 
H = tf([-4 48 -18 250 600],[1 30 282 525 60]); nichols(H) ngrid 

The right-click menu for Nichols charts includes the Tight option under Zoom. You can use this to clip unbounded branches of the Nichols chart.