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Let me preface this by saying that my background is pretty meagre (i.e. solid undergrad). However, a few months ago I came across this paper which presented an idea that struck me as really remarkable. One can develop a theory of analysis of functions taking values in an idempotent semiring (e.g. the max+ algebra), which happens to be naturally suited towards some traditionally nonlinear problems. Under this formulation (specialized to the case of max+), the integral of a good function corresponds to the supremum, the Fourier transform roughly corresponds to the Legendre transform (!), and it seems that one can develop a theory of "linear" (e.g. in terms of the max+ operations) PDE analogous to the traditional linear theory (!!). For example, the HJB equation is a nonlinear first order PDE, but linear in the max+ sense of the word. This all blew my mind, but after trying to read a few more papers on the subject I decided to put it on the back burner for later thought.

Then, a few days ago I was reading something written by Gian-Carlo Rota in which he makes a remark about developing an "algebra" for multisets. I guess distributive lattices model the "algebra" of sets well enough (in fact there is Birkhoff's theorem), but the quantitative aspect of multisets make this seem inappropriate. So just playing around a bit, I realize that if one models multisets on elements in X by functions from X to the nonnegative integers (the multiplicity), then multiset union corresponds to pointwise addition and multiset intersection corresponds to pointwise min. The min+ algebra on the nonnegative integers! Perhaps this points in the direction of why I think of tropical mathematics as something of interest to people in algebraic combinatorics (maybe this generalization is wrong).

Ok, sorry for that ramble. Essentially, I have 2 questions. First, aside from references to "dequantization", how should I envision the role of tropical mathematics? My lack of background makes it hard for me to get an idea of what is going on here (especially on the geometry side of things), but it seems like there are some big ideas lurking around.

Second, if I wanted to learn more about this stuff, what would be the best route to take? What expository papers should I look at / save for later? It's a bit intimidating that it seems like one needs background in algebraic geometry before one can seriously approach such ideas, but maybe that's just the way it is.

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4 Answers 4

Sturmfels/Speyer may be a good start. Otherwise I would look around on Arxiv particularly things that Dr. Bernd Sturmfels has written. Also, if you peruse his website (just look up Bernd Sturmfels + UC Berkeley), you'll probably get something interesting.

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For an overview of tropical geometry perhaps: A. Gathmann, Tropical algebraic geometry, Jahresbericht der DMV 108

It's available here.

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There is a short introduction by Mikhalkin: http://arxiv.org/abs/0709.1049 expanded in more detail in this book: http://www.math.toronto.edu/mikha/book.pdf

The Oberwolfach lecture notes by Itenberg, Mikhalkin and Shustin are also nice.

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If you're worried that you won't understand the geometric aspects, it might be worthwhile to check out the original papers of Simon -- it looks like most of the tropical ones are in English. Simon was, of course, primarily a computer scientist and combinatorialist, so while I haven't read those papers I suspect that the hardcore algebraic geometry stuff won't be there.

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