www.gusucode.com > robust 案例源码程序 matlab代码 > robust/DiskGainAndPhaseMarginsExample.m

    %% Disk Gain and Phase Margins
% 
%% 
% When you call |dmplot| without an argument, the
% resulting plot and text shows a comparison of a disk margin analysis with the
% classical notations of gain and phase margins. The Nyquist plot is
% of the loop transfer function L(s):
%%
% 
% $$L(s) = \frac{{\frac{s}{{30}} + 1}}{{(s + 1)({s^2} + 1.6s + 16)}}.$$
% 
dmplot
%%
% The _x_-axis corresponds to the gain variation in dB and the _y_-axis
% corresponds to the allowable phase variation in degrees. For a disk gain
% margin corresponding to 3 dB (1.414), the closed-loop system is stable
% for all phase and gain variations inside the blue ellipse. For example,
% the closed-loop system can simultaneously tolerate +/– 2 dB gain
% variation and +/– 14 deg phase variations.  To see the allowable
% variations for a given disk gain margin, use the given value as an input
% to |dmplot|.
figure           % new figure window
dmplot(1.414)