Could someone explain the meaning of this step function for me

Hi, I have obtained a code for simulating car suspension system using a LTI system x' = Ax + Bu, y = Cx+Du

m1 = 10;
m2 = 350;
kw = 500000;
ks = 10000;
Bb = [1000, 2000, 3000, 4000];
t = 0:0.1:2;

for i = 1:4
b = Bb(i);
A = [0 1 0 0; -(ks/m1+kw/m1) -b/m1 ks/m1 b/m1; 0 0 0 1; ks/m2 b/m2 -ks/m2 -b/m2];
B = [ 0; kw/m1; 0; 0];
C = [1 0 0 0; 0 0 1 0];
D = 0;

y = step(A,B,C,D,1,t); %Why is 1,t added?

subplot(2,2,i);
plot(t,y(:,1), ':', t, y(:,2), '-');
legend('Wheel', 'Car');
ttl = sprintf('Response with b = %4.1f' ,b);
title(ttl);
end

Can someone quickly explain to me why the step function is written in the way it is? Especially the part about the inclusion of 1 and t indices.

Answer 1

[Azzi Abdelmalek]

y = step(A,B,C,D,iu,t)

If your system has more then one imput, you can specify which one will be the step function, the others will be nuls.

In our case there is one input, then iu=1

t is a time vector

if you use

model=ss(A,B,C,D)
y = step(model,t); %t is time  vector

you will have the step response to the first input stored in y(:,:,1) and the responses to the second input in y(:,:,2)