# Using a bifurcation diagrams and time dependent parameters

Hello,

I'm lost at where to go after drawing bifurcation diagram of
$$\dot{x} = r + x - x^3.$$ If we also assume our parameter is time dependent such that
$$\dot{r} = -\delta x.$$ How could we use our initial bifurcation diagram to sketch solutions for small δ?

S.G. Janssens
Is there a reason why you would not want to consider the planar system
\left\{ \begin{aligned} \dot{x} &= r + x - x^3\\ \dot{r} &= -\delta x \end{aligned} \right.
in a neighborhood of ##(x, r) = (0,0)## and with (time-independent) parameter ##\delta## (which I suppose is small and positive)?

Another thing to note is that for time-independent ##r## the equation for ##\dot{x}## is the cusp normal form with parameters ##\beta_1 = r## and ##\beta_2 = 1##, but although I have heard of it, I am not sufficiently familiar with "slowly time-varying parameters" to see immediately how that normal form could provide an easier approach than when we just start with the planar system.

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I've gone through my "Strogatz's Nonlinear Dynamics and Chaos" and haven't found any problems like this, so I'm at a loss at how we can qualitatively sketch solutions. If $$\delta \approx 0,$$ then our parameter is almost constant for small x, though as x→±∞ we should eventually hit the bifurcations.