# ngrid

Superimpose Nichols chart on Nichols plot

## Description

example

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

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

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. ngrid returns a warning if the current axis does not contain a SISO Nichols frequency response.

ngrid('new') clears the current axes first and sets hold on.

ngrid(AX,___) plots the grid on the Axes or UIAxes object in the current figure with the handle AX. Use this syntax when creating apps with ngrid in the App Designer.

## Examples

collapse all

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

$H\left(s\right)=\frac{-4{s}^{4}+48{s}^{3}-18{s}^{2}+250s+600}{{s}^{4}+30{s}^{3}+282{s}^{2}+525s+60}.$

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

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

## Input Arguments

collapse all

Object handle, specified as an Axes or UIAxes object. Use AX to create apps with ngrid in the App Designer.