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    %% Sensitivity to Uncertain Elements
% Examine the relative sensitivity of the robust stability margin to the uncertain
% elements of the system. Consider a model of a control system containing 
% uncertain elements.
%%
k = ureal('k',10,'Percent',40);
delta = ultidyn('delta',[1 1]); 
G = tf(18,[1 1.8 k]) * (1 + 0.25*delta);
C = pid(2.3,3,0.38,0.001);
CL = feedback(G*C,1);
%%
% Create an options set for |robstab| that enables the sensitivity calculation.
opts = robOptions('Sensitivity','On');
%%
% Calculate the robust stability margin, specifying the |info| output to
% access additional information about the calculation.
[stabmarg,wcu,info] = robstab(CL,opts);
%%
% Examine the |Sensitivity| field of |info|.
info.Sensitivity
%%
% The values in this field indicate how much a change in the normalized
% perturbation on each element affects the stability margin.  For example,
% the sensitivity for |k| is 21. This value means that a given change |dk|
% in the normalized uncertainty range of |k| causes a change of about 21%
% percent of that, or |0.21*dk|, in the stability margin. The margin in
% this case is much more sensitive to |delta|, for which the margin changes
% by about 81% of the change in the normalized uncertainty
% range.