close all
clear all 
clc

t = -4:.01:5;
s = square_wave(t,3,.3);
figure
plot(t,s)
grid on
xlabel('time [s]')
title('square-wave')
axis([xlim -.1 1.1])

% printing figure in png format
set(gcf,'PaperUnits','inches','PaperPosition',[0 0 4 3])
print -dpng exercise3.png -r100

function s = square_wave(t,Tp,d)
t1 = mod(t/Tp,1); 
s = rect(t1/d) + rect((t1-1)/d);
end

function s = rect(t)
s = (abs(t)<.5)+.5*(abs(t)==.5);
end