how to obtain the parameters of the step response within matlab in open loop?
An example system and its step response:

s = tf('s');
SYS = 1/(s^2+s+1);
[Y,time] = step(SYS);


For K, use the final value of Y.

K = Y(end);


For L and T, use an amplitude threshold criteria. Here I consider L to be when amplitude goes above 5% the final value, and T when it goes above 63%.

L_index = find(Y&gt;=.05*K,1);
L = time(L_index);
T_index = find(Y&gt;=(1-exp(-1))*K,1);
T = time(T_index);


Use diff twice to detect the inflexion point, determine tangential line slope and the negative of its linear coefficient is equal to A.

D = diff(Y)./diff(time);
inflex = find(diff(D)./diff(time(1:end-1))&lt;0,1);
A = D(inflex)*time(inflex)-Y(inflex);


Now a plot to prove all is in order.

tangent = D(inflex)*time - A;
step(SYS), hold on, plot(time,tangent), plot(L,Y(L_index),'*'), plot(T,Y(T_index),'*')