Looping Error: subscript indices must either be real positive integers or logicals

x=(7*pi)/4
k=12  

for n = 1:k
      cossum(x) = ((-1^(n))*(x.^(2*n)))/(factorial(2*n));
end

When x is a fraction I get the subscript indices error. When its a whole number I do not. How to I run this loop with x as a decimal?

Answer 1

[Guillaume]

For a start x does not vary in the loop, so you'd be storing the result of the loop always in the same element of cossum. Secondly, you must use integer indices as the error message says. There's no reason to use x as an index in any case. I assume that's what you wanted:

x=(7*pi)/4
k=12    
for n = 1:k
      cossum(n) = ((-1^(n))*(x.^(2*n)))/(factorial(2*n));
end

Note that you don't need a loop in the first place. You can use vectorised operations:

x=(7*pi)/4;
k=12;
n = 1:k;
cossum = ((-1.^n)*(x.^(2*n))) ./ factorial(2*n)