# how do i know if a differential equation leads to chaos or catastrophe

When I use catastrophe here, I mean a system exhibiting a finite number of bifurcations and by chaos, I mean a system exhibiting a large(very) number of bifurcations.

I do know that catastrophe theory is based on Thom's theorem and chaos theory on qualitative analysis but I can't get over the fact that they are 2 different theories. They seem so similar in terms of bifurcations.

So, which theory do I use before-hand to know if a differential equation leads to chaos or catastrophe and furthermore, can you please explain the exact difference?

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I think bifurcations (at least in discrete-time dynamics) refer to an abrupt change in dynamics when you vary the parameters (so it makes sense to talk about bifurcations for a family of dynamical systems, but not for a single dynamical system). It doesn't seem to be what you mean though. – Glougloubarbaki Feb 3 '13 at 15:21
Glougloubarbaki-"so it makes sense to talk about bifurcations for a family of dynamical systems, but not for a single dynamical system"-but,take for example the spruce-budworm model,isn't that a single system with a perturbation function?It still exhibits abrupt changes(and hysteresis) when the parameters of the perturbation functions are changed.The thing I don't get is why is chaos theory so sensitive to initial conditions than parameter changes? – Sunny Marella Feb 5 '13 at 3:29

I am not familiar with catastrophe theory but would like to comment on the 'chaos' part. Apriori, it is only in very simple systems that you can know if there will be chaos. Over the last 100 years, there have been many tools developed to analytically and computationally find out if a given parameterized systems is chaotic. E.g.:

1). Melnikov's method

2). Thurston-Nielsen classification of diffeos on surfaces

3). Detection of horseshoes.

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thank you nonlinearism. Since your not too familiar with catastrophe theory,I can tell you that it is a branch of bifurcation theory and uses the principles of singularity-applied to a taylor series of a function.Although I'm not too familiar with the usage of potential functions,catastrophe theory uses Lyapunov functions to decide the stability of equilibrium,much like a ball on a hill/a valley. – Sunny Marella Feb 5 '13 at 3:25

When you apply catastrophe theory, you basically make Taylor expansions of your equations close to a bifurcation point and study how the parameters affect the behaviour. Then, according to the mathematical structure of your expansions, called "germs", you might reach conclusions about the behaviour of your system close to the bifurcation points.

In a more general sense, as explained in Robert Gilmore's excellent book, catastrophe theory is a "program", in the sense that it attempts to study how the qualitative nature of the solutions of equations depends on the parameters. Although in its more general form catastrophe theory deals with any discontinuity, there are in practice insurmountable difficulties with the most general equations. In practice, what has been done to a some extent successfully is to study the discontinuities of simple gradient dynamical systems. One aspect that might explain why catastrophe theory fell into almost oblivion is the silly turmoil about it in the 70's. Another, and more important, is that catastrophe theory does not suit itself very adequately to quantitative prediction and calculation, like applied dynamical systems, although it can be used for that.

Without claiming any expertise, I have been a fan of this branch of mathematics since about 2005, literally devouring books and articles. Arcane as it seems, catastrophe theory is an illuminating and very deep set of ideas, very closely related to topology, chaos and dynamical systems in general. I would recommend the above mentioned book to anyone interested in such things. Interested people might want to look to the above mentioned book, and also Poston and Stewart's, that has an excellent and gentle introduction. Of course, there is the very hard to digest original: Structural stability and morphogenesis. Vladimir Arnold wrote a very good book on the subject, which might appeal better to modern mathematicians. Enjoy!

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