Cannot get factorial loop to work! Do not know command...

The question is evaluate the following series: 1^2 + 2^2 +3^2 ... + 100^2. The answer is suppose to be 338350 but the only code i can get working is

a=[1:100] b=2; y=a.^b for y=1:length(a) end

which gives me each columns value, but does not add it up to value 338350! I have tried everything for a whole week please help :(

Answer 1

[Mischa Kim]

Use

a = [1:100];
b = 2; 
y = 0;
for ii = 1:length(a) 
  y = y + a(ii)^b;
end

display(y);

Your sum, y, needs to be inside the loop to be updated. Alternatively, you can make use of MATLAB's matrix operations

y = sum([1:100].^2);

[S]

Yay it works, thanks!

[John D'Errico]

Noe that the internal brackets [] are slightly bad, in the sense that they may make your code slightly less efficient. Use () there instead, so

y = sum((1:100).^2);

is better. Not a major issue, but one to remember. If you don't really need brackets, which will result in an extra function call overhead that was never needed, don't use them. Use parens instead. I'm pretty sure that mlint flags this issue.

[John D'Errico]

Another option here would be

y = dot(1:100,1:100);

Answer 2

[Roger Stafford]

Yet another way is:

 n = 100;
 y = n*(n+1)*(2*n+1)/6;