Finding the Bug
In this particular code, Ts is equal to 1/13. Which points that it will only draw 14 points and it is way too little for making a graph. In order to fix it, we need to give points more frequently by decreasing Ts (time period).
F0 =13; T0 =1/F0; Ts = 0.000001; % It was 0.07 before t = 0:Ts:13*T0; x = real(exp(j*(2*pi*F0*t-pi/2))); plot(t,x)
