MATLAB: For loop not calculating properly

for loophomeworksum

My instructions are to calculate the result and absolute error for each partial sum: N = 10, 160, and 640. I am supposed to be getting the sum and error value for each N, but I am only getting the sum and error values for 640 only. I do not know why this is the case, as N equals 10, 160 and 640.
PLEASE DO NOT GIVE ME A COMPLETE ANSWER. I WOULD JUST LIKE TO KNOW WHAT I AM DOING WRONG. THANK U.
This is what I have so far:
for N=[10 160 640]
    sum=0;
    for n=1:N
        y=1/n^2
        sum=sum+y;
    end
    sum
    error=((pi^2)/6)-sum
 end

Best Answer

Don't use sum as the name of your variable since that's already the name of a built-in function.
You need to assign N outside the loop and then get it inside the loop (method 1), OR use a counter to get the iteration number (method 2). 
N=[10 160 640] % Method 1
for k = 1 : length(N)
    thisN = N(k)
    % more code to compute this sum.
end
Then you need to compute thisSum(k) and also index the error with the iteration loop counter:
thisError(k) = ((pi^2)/6) - thisSum(k);
so that you will have an error value for every iteration.
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