Bugged Code
F0 =13; T0 =1/F0; Ts = 0.07; t = 0:Ts:13*T0; x = real(exp(j*(2*pi*F0*t-pi/2))); plot(t,x)
Unbugged
The sampling rate is the same as the frequency, doing this will not plot the proper amount of cycles. By decreasing the sampling rate we will get a much more accurate plot.
F0 =13; T0 =1/F0; Ts = 0.001; t = 0:Ts:13*T0; x = real(exp(j*(2*pi*F0*t-pi/2))); plot(t,x)