Much more helpful if you copy/paste the entire error as well as the code.
My initial guess is that you are getting an error that the index must be a positive integer? In your for loop, your loop counter i starts at 1. In you conditional statement on line 10, you use x(i-1). When i=i, it attempts to extract the value at x(0). However, in MATLAB, indexing starts at 1, not 0.
The simplest solution is to have your for loop index start at 2.
