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 and results in poor resolution. 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)
