We can use Matlab to help to work through the trigonometry The angle contribution of the plant and feedback at S, is obtained as follows G=tf(1,[1,0,0]); 1 GH G*Hi s1=-2+2j; The total contribution of the plant poles and zeros can be calculated directly using the Matlab equivalent of the angle criterion ∠G(s)H(s) ∑4(s1-=)-∑∠(s1-p) (6.11) S=SI 2022-2-11 152022-2-11 15 We can use Matlab to help to work through the trigonometry. The angle contribution of the plant and feedback at s1 is obtained as follows. G = tf(1,[1,0,0]); H = 1; GH = G*H; s1 = -2+2j; The total contribution of the plant poles and zeros can be calculated directly using the Matlab equivalent of the angle criterion             m j n i j i s s G s H s s z s p 1 1 1 1 ( ) ( ) ( ) ( ) 1 (6.11)