# Asymptotic series

I have found many references to Poincaré and Borel in relation to their work on asymptotic series, but so far, every source I can get my hands on is very old, hence hard to read (this is not true in general, but in this case, texts that predate Oh notation tend not to be clear).

Can you explain the idea behind asymptotic series, give an illuminating example, and/or suggest a good modern exposition of the theory?

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Web pages of

Michael Berry: http://www.phy.bris.ac.uk/people/berry_mv/dingle.html

and

John Boyd: http://www-personal.umich.edu/~jpboyd/

both include helpful published and publicly available sources.

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Basically what I was hoping for... Thanks! –  Rodrigo A. Pérez May 2 '13 at 12:10

There are many modern books, for example,

MR1317343 Balser, Werner From divergent power series to analytic functions. Theory and application of multisummable power series. Lecture Notes in Mathematics, 1582. Springer-Verlag, Berlin, 1994.

MR1250603 Candelpergher, B.; Nosmas, J.-C.; Pham, F. Approche de la résurgence. Actualités Mathématiques. Hermann, Paris, 1993.

The very basic idea is the following: You frequently obtain divergent series, a) as formal solutions of differential (or functional) equations, b) as perturbation series when you vary a linear operator.

The question is whether these series have any relation to actual solutions of the problem. It often turns out that they are asymptotic series, and moreover, that they are "Borel summable". Borel summation is a procedure using a form of Laplace transform that under certain conditions recovers the function from its formal asymptotic series.

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