Bug Explaination
The problem for this system is that the sampling freqeuncy is too low for the graph. Ts only manage to sample one or 2 dots in a single sin wave. By increasing the value for Ts, the complete graph can be shown
F0 =13; T0 =1/F0; Ts = 0.07/1000000; t = 0:Ts:13*T0; x = real(exp(j*(2*pi*F0*t-pi/2))); plot(t,x)
Graph
