Record iterations of loop that has a constant numel

I have a loop that cycles through time advancing 126 days each time to calculate returns of stock prices. I would like to record the returns at each interval, however, since the number of element in the loop remains constant, I am getting an index out of bounds error. Any idea to how to fix that? Here is a sample of my code (the actual one is quite a bit longer):

for z = 1:126:883
[num, txt] = xlsread('GDX_ETF_Sector_MeanRev.xlsx', 'GLD');
start = strmatch('5/31/2006', txt(1:end), 'exact')+z;
finish = start+252;
[num, txt] = xlsread('GDX_ETF_Sector_MeanRev.xlsx', 'GLD', ['A' num2str(Istart) ':B' num2str(finish)'']);
returns = price2ret(num);
end

If I change it to returns(z) I get an error: In an assignment A(I) = B, the number of elements in B and I must be the same. If I fix this error then I get index out of bounds because numel in z remains constant.

Thanks a lot for your help!

Answer 1

[Tom]

It's not entirely clear to me, but it looks like the variable num will have a length of 252. I think the best way would be to store it in a large matrix, or a cell:

count=0;
for z = 1:126:883
count=count+1;
...
returns{count}=price2ret(num);

or

returns(count,:)=price2ret(num);
end

[Noah]

Works perfectly, thanks a lot!