def A_func(*, η_O, η_A, η_H, b_θ, b_r, b_φ, deriv_η_O, deriv_η_A, deriv_η_H,
    deriv_b_θ, deriv_b_r, deriv_b_φ):
    """
    Compute the value of the variable A
    """
    return (deriv_η_H * b_θ + η_H * deriv_b_θ - deriv_η_A * b_r * b_φ - η_A *
        deriv_b_r * b_φ - η_A * b_r * deriv_b_φ) / (η_O + η_A * (1 - b_φ ** 2)
        ) - (deriv_η_O + deriv_η_A * (1 - b_φ ** 2) - 2 * η_A * b_φ * deriv_b_φ
        ) * (η_H * b_θ - η_A * b_r * b_φ) / (η_O + η_A * (1 - b_φ ** 2)) ** 2
