def dderiv_v_r_midplane(a_0, v_r, v_φ, deriv_B_r, deriv_B_φ, dderiv_B_θ, γ,
    η_perp_sq, η_H, η_P, Y_6, Y_5, Y_4, Y_3, Y_2, Y_1):
    """
    Compute v_r'' around the midplane
    """
    return (v_φ * Y_4 / Y_5 + 4 * γ ** 2 * v_r ** 2 + a_0 / 2 * (dderiv_B_θ *
        deriv_B_r + 2 * deriv_B_φ ** 2 * (1 / 4 - γ) + Y_3 - Y_2 * η_H /
        η_P + η_H * Y_4 / (η_perp_sq * Y_5) + 2 * dderiv_B_θ * (1 / 4 - γ) +
        Y_1 * (deriv_B_r + 1 / 4 - γ))) / Y_6
