def Nyquist((A, B, C, D), T):
    sys = ss(A, B, C, D)
    real, imag, freq = nyquist(sys, omega=arange(T[0], T[1], T[2]), Plot=False)
    plot(real, imag)
    title('Nyquist construction')
    xlabel('Real')
    ylabel('Imag')
    grid(color='g', linestyle='--')
    show()