You can compute the describing function for saturation nonlinearity using FRESTIMATE
over the same set of amplitudes for a fixed frequency of 5 rad/s. Note that the describing
function of saturation does not depend on frequency, thus it is sufficient to run the
analysis at a single frequency. Run a loop over all amplitudes where you will create a
sinestream input with the (fixed) frequency and given amplitude, then run FRESTIMATE
using this input signal at each iteration.
w = 5;
io(1) = linio('scdsaturationDF/In1',1,'input');
io(2) = linio('scdsaturationDF/Saturation',1,'output');
N_A_withfrest = zeros(size(N_A));
for ct = 1:numel(A)
in = frest.Sinestream('Frequency',w,'Amplitude',A(ct));
sysest = frestimate(mdl,in,io);
Describing Function Analysis of Nonlinear Simulink Models