def dot_product(u, v):
    """
    return the vector dot-product between equal length vectors.

    :param u: list of numbers(vector)
    :param v: list of numbers(vector)
    :return: the dot-product
    """
    i = 0
    result = 0
    for index in u:
      result += index * v[i]
      i += 1
    return result