What is the value of n?
The most obvious thing to me is that your for loop doesn't actually run, so x is never created.
The loops don't run because you start at k=n-1 and ends when k=1. You're not getting an error that your index has to be positive, so n>=2. If x is not created at all, that means n>=3, causing to loop indices to be 2:1, resulting in an empty array, which means your loop never runs.
