English

A curious identity in connection with saddle-point method and Stirling's formula

Combinatorics 2022-10-21 v1 Classical Analysis and ODEs

Abstract

We prove the curious identity in the sense of formal power series: [ym]exp(t22+j3(it)jj!yj2)dt=[ym]exp(t22+j3(it)jjyj2)dt, \int_{-\infty}^{\infty}[y^m] \exp\left(-\frac{t^2}2 +\sum_{j\ge3}\frac{(it)^j}{j!}\, y^{j-2}\right)\mathrm{d} t = \int_{-\infty}^{\infty}[y^m] \exp\left(-\frac{t^2}2+ \sum_{j\ge3}\frac{(it)^j}{j}\, y^{j-2}\right)\mathrm{d} t, for m=0,1,m=0,1,\dots, where [ym]f(y)[y^m]f(y) denotes the coefficient of ymy^m in the Taylor expansion of ff. The generality of this identity from the perspective of saddle-point method is also examined.

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Cite

@article{arxiv.2210.10989,
  title  = {A curious identity in connection with saddle-point method and Stirling's formula},
  author = {Hsien-Kuei Hwang},
  journal= {arXiv preprint arXiv:2210.10989},
  year   = {2022}
}

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