Added code for computing tau and Tar.

getTauTar.m

+% The relative dead time tau = L/(L+T) and arrest time Tar = T+L are
+% defined for first order time delayed SISO LTI systems
+%P(s) = K/(s*T+1)*exp(-s*L)
+%
+% This code computes generalizations of tau and Tar for arbitrary SISO LTI
+% systems, which can be either discrete or continuous.
+% Written by kristian@control.lth.se
+% Downloaded from git@gitlab.control.lth.se:kristian/PIDopt.git
+
+function [tau,Tar,L] = getTauTar(P)
+[~,t] = step(P);
+t = linspace(0,t(end),1e5);
+[y,t] = step(P,t);
+ydot = impulse(P,t);
+[~,i] = max(ydot);
+tmax = t(i);
+ymax = y(i);
+L = tmax-ymax/ydot(i);
+if dcgain(P) == inf
+    tau = 0;
+    Tar = inf;
+    return 
+end
+P = P/dcgain(P);
+if P.Ts > 0
+    P = d2c(P,'zoh')
+end
+Tar = sum(-1./pole(P))-sum(-1./zero(P))+totaldelay(P);
+T = Tar-L;
+tau = L/Tar;
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