function [y,t,x] = step_RPT(sys, final_time, step_val, step_time)
if nargin<3
    step_val = 1;
end
if nargin<4
    step_time = 0;
end
t = linspace(0, final_time, 5000);
u  = zeros(size(t));
u(t>=step_time) = step_val;
[y,t,x] = lsim(sys, u, t);