Hi Mohammed,
I understand that you want to plot the following discrete equation.This can be achieved by leveraging the "stem" function which is used for plotting discrete sequence data.
n = (-20:20); % defining range of n
u_n = (n>=0); % unit step function
tiledlayout(3,1);
nexttile; % u[n]
stem(n,u_n);
nexttile; % e^-n
stem(n,exp(-n));
nexttile; % u[n]*e^-n
stem(n,u_n.*exp(-n));
For more information about the "stem" function, have a look at the following reference
I hope this helps
