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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

H1+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

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

H(s)=-4s4+48s3-18s2+250s+600s4+30s3+282s2+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

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

See Also

Introduced before R2006a