def METHOD_NAME(self, parents_params: np.ndarray) -> np.floating:
    # The line connecting x1 to x2 is called psl (primary search line).
    # Compute the 2-norm of the vector orthogonal to psl from x3.
    e_12 = UNDXCrossover._normalized_x1_to_x2(
        parents_params
    )  # Normalized vector from x1 to x2.
    v_13 = parents_params[2] - parents_params[0]  # Vector from x1 to x3.
    v_12_3 = v_13 - np.dot(v_13, e_12) * e_12  # Vector orthogonal to v_12 through x3.
    m_12_3 = np.linalg.norm(v_12_3, ord=2)  # 2-norm of v_12_3.
    return m_12_3