For loop not calculating properly

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

[David Hill]

You could vectorize the whole thing.

n=1:640;
s=cumsum(1./(n.^2));
e=abs(pi^2/6-s);

[Kyle Donk]

I have to use a for loop for this and most of the time we are not allowed to use Matlab's built-in functions.

[Image Analyst]

Kyle, did you see my Answer (below)??? I already gave you hints for solving it using your current for loop.

Answer 1

[Image Analyst]

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.

[Image Analyst]

Kyle, did this solve it? If so, please accept this answer, and any other answers for your other questions/threads. Thanks in advance.