Help with for loop

I need help or direction on for loops given the question

Use a loop to create a vector vout that contains the 5‐value moving average of vin.  Since it takes 5 values of input to create the first value in the output, there will be a slight delay in the output.  In other words, the first non‐zero value of vout will occur at the 5th position of vout and will be the average of vin(1) through vin(5).

given information

    f1 = 100; % The lower frequency in cycles per second
    f2 = 400; % The higher frequency in cycles per second
    w1 = 2*pi*f1; % The lower frequency in radians per second
    w2 = 2*pi*f2; % The higher frequency in radians per second
    T1 = 1/f1; % The period of the lower frequency 
    T2 = 1/f2; % The period of the higher frequency
    ns = 20; % Number of samples per period of high freq. component
    % Plot the signal over 4 periods of the lower frequency component. The
    % increment of the composite signal will be the period of the higher
    % frequency component divided by ns.
    t = (0:T2/ns:4*T1);
    vin = cos(w1.*t) + cos(w2.*t);
    vout(k) = (vin(k) + vin(k-1) + vin(k-2) + vin(k-3) + vin(k-4) ) / 5

This is what i tried

    for k= 5:90;
        vout(k) = (vin(k) + vin(k-1) + vin(k-2) + vin(k-3) + vin(k-4) ) / 5
    end
    plot(k,vin)
    plot(k,vout)

[Guillaume]

Your loop is fine (assuming that there's 90 elements in vin), so what is your problem?

I wouldn't hard code the upper bound and would use numel(vout) instead.

Your plot look weird, the first argument (k) is scalar but that has nothing to do with the for loop.

[benny]

I dont get anything on the graph, my values for vin were guessed

[Guillaume]

plot(vin);
plot(5:numel(vout), vout);

should solve that (assuming hold all). But again, that has nothing to do with the loop. Since your question is about the loop, again, what problem are you having with it?

Answer 1

[Andrei Bobrov]

f1 = 100;
f2 = 400;
w1 = 2*pi*f1;
w2 = 2*pi*f2;
T1 = 1/f1; 
T2 = 1/f2; 
ns = 20; 
t = (0:T2/ns:4*T1);
vin = cos(w1.*t) + cos(w2.*t);
vin = vin(:);
out = conv2(vin,ones(5,1)/5,'valid');

with loop

out = zeros(numel(vin)-4,1);
for jj = 1:numel(vin)-4
    out(jj) = mean(vin(jj:jj+4));
end

plot:

plot([vin(5:end), out])

Answer 2

[MA]

you have common mistakes,here your correct code:

clear all
close all
clc;
    f1 = 100; % The lower frequency in cycles per second
    f2 = 400; % The higher frequency in cycles per second
    w1 = 2*pi*f1; % The lower frequency in radians per second
    w2 = 2*pi*f2; % The higher frequency in radians per second
    T1 = 1/f1; % The period of the lower frequency 
    T2 = 1/f2; % The period of the higher frequency
    ns = 20; % Number of samples per period of high freq. component
    % Plot the signal over 4 periods of the lower frequency component. The
    % increment of the composite signal will be the period of the higher
    % frequency component divided by ns.
    t = (0:T2/ns:4*T1);
    vin = cos(w1.*t) + cos(w2.*t);
    for k=5:90
        vout(k) = (vin(k) + vin(k-1) + vin(k-2) + vin(k-3) + vin(k-4) ) / 5;
    end
    k=5:90;
    voutn(1,:)=vout(5:90);
    subplot(2,1,1)
    plot(t,vin)
    title('vin')
    subplot(2,1,2)
    plot(k,voutn)
    title('vout')