compute sums by accumulating in a for-loop

I am trying to accumulate sums (phi(l) for lags " l"in a for loop given the code below. I keep getting "Unable to perform assignment because the left and right sides have a different number of elements." I have tried multiple ways to try and fix it but nothing is working.

x=normrnd(0,1,100,1);
xprime=detrend(x,'constant');
phi=zeros(14,1);
L= [0:13]';
for l=1:14
    phi(l)=(sum(xprime(1:100-l)).*xprime(1+l:100)/(100-(l-1)-1));
end  

Unable to perform assignment because the left and right sides have a different number of elements.

Answer 1

[Image Analyst]

Look at this:

x=normrnd(0,1,100,1);
xprime=detrend(x,'constant');
phi=zeros(14,1);
L= [0:13]';
for l=1:14
    temp = (sum(xprime(1:100-l)).*xprime(1+l:100)/(100-(l-1)-1))
    fprintf('The size of temp = %d.\n', numel(temp))
    phi(l)=(sum(xprime(1:100-l)).*xprime(1+l:100)/(100-(l-1)-1));
end  

temp = 99×1

0.0116 0.0105 0.0110 0.0077 -0.0046 -0.0012 -0.0141 0.0183 0.0027 -0.0052

The size of temp = 99.

Unable to perform assignment because the left and right sides have a different number of elements.

So you're trying to stuff 99 values into a slot meant for only one value, phi(l). Not sure how to fix it because I'm not sure what your intent is. Did you mean for phi to be a 99 by 14 matrix and you want to put temp into the columns of phi?

[Kyle]

Instead of making seperate lines for each element or lag (l). I am trying to create a loop in which if you substite each value of l(1-14) you will get the cumulative sum.

i.e

l=1

phi(l)=(sum(xprime(1:100-l)).*xprime(1+l:100)/(100-(l-1)-1));

l=2

phi(l)=(sum(xprime(1:99)).*xprime(2:100)/(100-(l-1)-1));

etc..

[Image Analyst]

Watch your parentheses. Maybe you meant either

phi(l) = sum(xprime(1:(100-l)) .* xprime(l:100) / (100-(l-1)-1));

or

phi(l) = sum(xprime(1:(100-l) .* xprime(l:100)) / (100-(l-1)-1);

And l (ell) is not a good variable name - it looks too much like 1 (one) and I (capital I). Use k instead.

[Kyle]

This worked thank you.

Answer 2

[Torsten]

sum(xprime(1:100-l))

This is a scalar.

sum(xprime(1:100-l)).*xprime(1+l:100)

This is a vector of length 100-(1+l)+1.

(sum(xprime(1:100-l)).*xprime(1+l:100)/(100-(l-1)-1))

This remains a vector of length 100-(1+l)+1.

phi(l)

This is s acalar.

Thus you try to assign a vector to a scalar which is not possible.

Maybe you mean

phi(l)=sum(xprime(1:100-l).*xprime(1+l:100))/(100-(l-1)-1));