Return the largest real value h such that all elements in x are integer
    multiples of h.

def _gcd_array(X):
    """
    Return the largest real value h such that all elements in x are integer
    multiples of h.
    """
    greatest_common_divisor = 0.0
    for x in X:
        greatest_common_divisor = _gcd(greatest_common_divisor, x)

    return greatest_common_divisor