John, you just need to build the signal (no need for plotting), e.g.,
dt = 0.1; % adjust as necessary
t = 0:dt:50;
u = zeros(1,numel(t));
u(t<=20) = 45; % you probably want to use rad instead of deg
u(t> 20 & t<=40) = -45;
u(t> 40) = 0;
and feed it as an input to the system.
