Asymptotics of multivariate sequences II: multiple points of the singular variety. Pemantle, R. & Wilson, M. C. Combinatorics, Probability and Computing, 13(4-5):735-761, Cambridge University Press, 2004.
Asymptotics of multivariate sequences II: multiple points of the singular variety [link]Paper  abstract   bibtex   
Let $F(\b{z})=∑_\b{r} a_\b{r}\b{z^r}$ be a multivariate generating function which is meromorphic in some neighborhood of the origin of $ℂ^d$, and let $\mathcal{V}$ be its set of singularities. Effective asymptotic expansions for the coefficients can be obtained by complex contour integration near points of $\mathcal{V}$. In the first article in this series, we treated the case of smooth points of $\mathcal{V}$. In this article we deal with multiple points of $\mathcal{V}$. Our results show that the central limit (Ornstein-Zernike) behavior typical of the smooth case does not hold in the multiple point case. For example, when $\mathcal{V}$ has a multiple point singularity at $(1 , … , 1)$, rather than $a_\b{r}$ decaying as $|\b{r}|^{-1/2}$ as $|\b{r}| \to ∞$, $a_\b{r}$ is very nearly polynomial in a cone of directions.
@article{pemantle2004asymptotics,
  title={Asymptotics of multivariate sequences II: multiple points of the singular variety},
  author={Pemantle, Robin and Wilson, Mark C.},
  journal={Combinatorics, Probability and Computing},
  volume={13},
  number={4-5},
  pages={735-761},
  year={2004},
  publisher={Cambridge University Press},
  keywords={ACSV theory},
  url_Paper={https://www.cambridge.org/core/journals/combinatorics-probability-and-computing/article/abs/asymptotics-of-multivariate-sequences-ii-multiple-points-of-the-singular-variety/F8B144EBED2754E43361A3BE4B0C3B01},
  abstract={Let $F(\b{z})=\sum_\b{r} a_\b{r}\b{z^r}$ be a multivariate  generating
function which is meromorphic in some neighborhood of the origin of
$\mathbb{C}^d$, and let $\mathcal{V}$ be its set of singularities.
Effective asymptotic expansions for the coefficients can be obtained by
complex contour integration near points of $\mathcal{V}$. In the first
article in this series, we treated the case of smooth points  of
$\mathcal{V}$. In this article we deal with multiple points of
$\mathcal{V}$. Our results show that the central limit
(Ornstein-Zernike) behavior typical of the smooth case does not hold in
the multiple point case. For example, when $\mathcal{V}$ 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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