def v_atm_n(f, t, alpha, beta, rho, volvol):
    """Debug function - to remove"""
    f_av = f
    A = -beta * (2 - beta) * alpha ** 2 / (24 * f_av ** (2 - 2 * beta))
    B = rho * alpha * volvol * beta / (4 * f_av ** (1 - beta))
    C = (2 - 3 * rho ** 2) * volvol ** 2 / 24
    v_atm_n = alpha * f ** beta * (1 + (A + B + C) * t)
    return v_atm_n
