How to plot sine wave with given number of cycles?

I was given a question in class to plot sine wave x(t)=A_1*sin(2*π*f_1*t+θ_1 )+A_2*sin(2*π*f_2*t+θ_2 )+A_3*sin(2*π*f_3*t+θ_3 ) with number of cycles as a user input. Please help me!

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer

Answer 1

[Abraham Boayue]

clear variables
close all

% Define the amplituted vector
A_1 = 1;
A_2 = 2;
A_3 =3;
A =[A_1 A_2 A_3];

% Choose the phase in radians
q_1 = pi/2; 
q_2 = pi/4; 
q_3 = pi/8;
theta = [q_1 q_2 q_3];

% Choose the frequency in Hz
f_1 = 1; 
f_2 = 2; 
f_3 = 3;
f = [f_1 f_2 f_3];

disp('   ')
disp(' Enter the time circle between, (choose b higher than a) a and b  ');
a = input (' In the form [a b]    '); % enter [-2 2] for example
disp('   ')

M = 500;  % Take 500 samples of the function the, higher the better
t = a(1):4/(M-1):a(2);
y = zeros(1,M);

N = 3; % Number of terms in x(t)
for k = 1:N 

      y = y+ A(k)*sin(2*pi*f(k)*t+theta(k));

end

plot(t,y,'linewidth',2,'color','m')
a= title('x(t) : sum of sine waves');
set(a,'fontsize',14);
a= xlabel('t [-2 2]');
set(a,'fontsize',20);
a = ylabel('y');
set(a,'fontsize',20);
a = zlabel('z');
set(a,'fontsize',20);
grid

[Abraham Boayue]

Please accept my answer if you find it right. Good luck.

Answer 2

[Abraham Boayue]

t = a(1):(a(2)-a(1))/(M-1):a(2);

[Abraham Boayue]

Replace the expression for t in full code with the one above to improve the quality of the program; if not, it will only work for the vector [-2 2].