def parabolic_turning_point(y):
    """
    Find the location of the turning point for a parabola
    ``y(x) = ax^2 + bx + c``, given input values ``y(-1), y(0), y(1)``.
    The maximum is located at ``x0 = -b / 2a``. Assumes
    that the input array represents an equally spaced sampling at the
    locations ``y(-1), y(0) and y(1)``.

    Parameters
    ----------
    y : `numpy.ndarray`
        A one dimensional numpy array of shape "3" with entries that sample the
        parabola at "-1", "0", and "1".

    Returns
    -------
    `float`
        A float, the location of the parabola maximum.
    """
    numerator = -0.5 * y.dot([-1, 0, 1])
    denominator = y.dot([1, -2, 1])
    return numerator / denominator
