Noob problem: Defining a fumction and passing values issues an error "Subscript indices must either be real positive integers or logicals."

I have the following function:

function [ result ] = SSD( i1, i2 )
if size(i1) == size(i2)
    [r, c] = size(i1)
    result = -(sum(sum((double(i1) - double(i2)).^2)) / (r*c));
else
    result = 'invalid';
end

I would like to pass it to images that contain gray values only and the error:

Subscript indices must either be real positive integers or logicals.

Popes up. For debugging purpuse I tried calling the function in this way:

SSD(zeros(3), ones(3));

The error is still there. But if I call the function in this way:

SSD(ones(3), ones(3));

No error. What is happening? Why doesn't the function like zero values?

Answer 1

[Jon]

Runs fine on my machine-no errors. 2015a. Do you have a variable named SSD or zeros?

[Kirby Fears]

Try clearing your workspace before calling SSD.

clear;
SSD(zeros(3), ones(3));

If this works, you probably had a variable named zeros in your workspace.

[Veselin Ivanov]

Aaaa. Thanks :). I cleaned the workspace and now it worked. I have to get used to that old variables hang around :).