Can someone explain why the top code works but the bottom one has an error that says "Index exceeds the number of array elements. Index must not exceed 1."

First Code:

f=@(x) ((2.*x)./((2.*x)-1)).*((2.*x)/((2.*x)+1));
k=1;s=f(1);
for k=2:1000
    s=s*f(k);
end
s

s = 1.5704

Second Code:

f=@(x) ((2.*x)./((2.*x)-1)).*((2.*x)/((2.*x)+1));
n=1;p=f(1);
for n=2:1000
    p=p*p(n);
end

Index exceeds the number of array elements. Index must not exceed 1.

p

Error code: Index exceeds the number of array elements. Index must not exceed 1.

I am trying to evaluate the following product but only for n=1:1000

[Stephen23]

The MATLAB approach:

n = 1:1000;
prod((4*n.^2) ./ (4*n.^2-1))

ans = 1.5704

Answer 1

[Stephen23]

"Can someone explain why the top code works but the bottom one has an error that says "Index exceeds the number of array elements. Index must not exceed 1.""

Take a look at the size of p:

f=@(x) ((2.*x)./((2.*x)-1)).*((2.*x)/((2.*x)+1));
p=f(1);
size(p)

ans = 1×2

1 1

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How many elements does it have? (hint: one)

What do you expect MATLAB to do when ask for the 2nd element of an array that has only one element in it? Because that is exactly what you are doing on the very first loop iteration, when you index into p like this: p(n).

Perhaps on this line

p=p*p(n);

you really intended to write this:

p=p*f(n);

% ^

[David]

such a simple mistake. Thank you very much I thought I was going crazy!