% Nise, N.S.
% Control Systems Engineering, 6th ed.
% John Wiley & Sons, Hoboken, NJ, 07030
% Control Systems Engineering Toolbox Version 6.0
% Copyright 2011 by John Wiley & Sons, Inc.
% (ch10p6): We can use MATLAB to plot Nichols charts using nichols(G),
% where G(s) = numg/deng and G is an LTI transfer-function object. The
% Nichols grid can be added using the ngrid command after the nichols(G)
% command. Information about the plots obtained with nichols(G) can be
% found by left-clicking the mouse on the curve. You can find the curve's
% label, as well as the coordinates of the point on which you clicked
% and the frequency. Right clicking away from a curve brings up a menu
% if the icons on the menu bar are deselected. From this menu you
% can select (1) system responses to be displayed and (2) characteristics,
% such as peak response. When selected, a dot appears on the curve at
% the appropriate point. Let your mouse rest on the point to read the value
% of the characteristic. You also may select (3) choice for grid on or off,
% (4) returning to full view after zooming, and (5) properties, such as
% labels, limits, units, style, and characteristics. Let us make a Nichols
% chart of G(s) = 1/[s(s+1)(s+2)].
'(ch10p6)' % Display label.
clf % Clear graph on screen.
numg=1; % Define numerator of G(s).
deng=poly([0 -1 -2]); % Define denominator of G(s).
'G(s)' % Display label.
G=tf(numg,deng) % Create and display G(s).
nichols(G) % Make a Nichols plot.
ngrid % Add Nichols grid.