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Asymptotics of Multivariate Sequences II: Multiple Points of the Singular Variety

Published online by Cambridge University Press:  24 September 2004

ROBIN PEMANTLE
Affiliation:
Department of Mathematics, Ohio State University, Columbus OH 43210, USA (e-mail: pemantle@math.upenn.edu) Current address: Department of Mathematics, University of Pennsylvania, Philadelphia, PA 19104-6395, USA.
MARK C. WILSON
Affiliation:
Department of Computer Science, University of Auckland, Private Bag 92019 Auckland, New Zealand (e-mail: mcw@cs.auckland.ac.nz)
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Abstract

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Let $F(\b{z})=\sum_\b{r} a_\b{r}\b{z^r}$ be a multivariate generating function that is meromorphic in some neighbourhood of the origin of $\mathbb{C}^d$, and let $\sing$ be its set of singularities. Effective asymptotic expansions for the coefficients can be obtained by complex contour integration near points of $\sing$.

In the first article in this series, we treated the case of smooth points of $\sing$. In this article we deal with multiple points of $\sing$. Our results show that the central limit (Ornstein–Zernike) behaviour typical of the smooth case does not hold in the multiple point case. For example, when $\sing$ has a multiple point singularity at $(1, \ldots, 1)$, rather than $a_\b{r}$ decaying as $|\b{r}|^{-1/2}$ as $|\b{r}| \to \infty$, $a_\b{r}$ is very nearly polynomial in a cone of directions.

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Type
Paper
Copyright
© 2004 Cambridge University Press