def dderiv_η_skw_midplane(*, dderiv_ρ, deriv_B_r, deriv_B_φ, dderiv_B_θ):
    """
    Compute the derivative of η assuming the same form as in SKW
    """
    return 2 * (deriv_B_r ** 2 + deriv_B_φ ** 2 + dderiv_B_θ) - dderiv_ρ
