The following MATLAB code has a bug in it:
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)
The bug is that Ts is far too large. Dividing by either 100 or 1000 will greatly improve the situation. The fixed code looks like
F0 =13; T0 =1/F0; Ts = 0.0007; t = 0:Ts:13*T0; x = real(exp(j*(2*pi*F0*t-pi/2))); plot(t,x)
Or
F0 =13; T0 =1/F0; Ts = 0.00007; t = 0:Ts:13*T0; x = real(exp(j*(2*pi*F0*t-pi/2))); plot(t,x)