octave:13> num = [1]
num =  1
octave:14> den = [1 1]
den =

   1   1

octave:15> sys = tf(num, den)

Transfer function 'sys' from input 'u1' to output ...

	1
 y1:  -----
      s + 1

Continuous-time model.
octave:16> margin(sys)
octave:17> [Gm, Pm, Wcg, Wcp] = margin(sys)
Gm = Inf
Pm =  180
Wcg = NaN
Wcp = NaN
octave:18> nyquist(sys)
octave:20> Gm
Gm = Inf