I would like a plot of the instantaneous phase difference between a frequency-swept drive and the nonlinear oscillator it is driving. x[t] below is the instantaneous displacement of the oscillator and plotx provides a plot. 

Thanks,
Carey

```
s =
 NDSolve[{x''[t] + x[t] - 0.167 x[t]^3 == 
    0.005 Cos[t - 0.5*0.0000652*t^2], x[0] == 0, x'[0] == 0}, 
  x, {t, 0, 3000}, MaxSteps -> 35000]

plotx = Plot[Evaluate[x[t] /. s], {t, 0, 3000}, PlotPoints -> 10000, 
  Frame -> {True, True, False, False}, FrameLabel -> {"t", "x"}, 
  FrameStyle -> Directive[FontSize -> 15], PlotLabel -> "(a)", 
  Axes -> False]

```