Unit impulse using MATLAB

MATLAB Code:
%unit impulse
n=-10:20 ;
us=[zeros(1,10) ones(1,21)];
subplot(3,1,1);
stem(n,us);
title('unit step')
axis([-10 20 0 1.2]);
delayed unit step

MATLAB Code:

%delayed unit impulse
n=-10:20;
usd=[zeros(1,15) ones(1,16)];
subplot(3,1,2);
stem(n,usd);
title('delayed unit step')
axis([-10 20 0 1.2]);

MATLAB Code:

%advanced unit step
n=-10:20 ;
usa=[zeros(1,3) ones(1,28)];
subplot(3,1,3);
stem(n,usa);
title('advanced unit step ')axis([-10 20 0 1.2]);