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

H1+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(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 right-click menu for Nichols charts includes the Tight option under Zoom. You can use this to clip unbounded branches of the Nichols chart.

See Also

Introduced before R2006a