There is no zeroth element in a MATLAB array. Since you didn't describe your problem, it's hard to suggest any solution.
If you are trying to extract values "between" or "beyond" the discrete elements of an array, use interpolation tools like interp1() or interp2().
If you're trying to write a loop and you're trying to use a single variable (the loop iterator) for both indexing and numerical operations, don't. Separate that into a vector for numerical operations and then use the loop iterator for indexing.
