The non-central gamma sum and difference distributions: exact distribution and asymptotic expansions

Fuente: arXiv
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Autores principales: Gaunt, Robert E., Sutcliffe, Heather L.
Formato: Preprint
Publicado: 2026
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author Gaunt, Robert E.
Sutcliffe, Heather L.
author_facet Gaunt, Robert E.
Sutcliffe, Heather L.
contents Exact formulas are derived for the probability density functions of the sum and difference of two independent non-central gamma distributed random variables, with both series and integral representations of the density presented. These formulas are then applied to obtain asymptotic expansions for the probability density function, tail probabilities and quantile functions of these distributions. As a special case, we deduce asymptotic expansions for the probability density function of the product of correlated normal random variables with the coefficients given in closed-form. Numerical results are presented to assess the accuracy of our asymptotic approximations across a range of parameter constellations.
format Preprint
id arxiv_https___arxiv_org_abs_2605_15386
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle The non-central gamma sum and difference distributions: exact distribution and asymptotic expansions
Gaunt, Robert E.
Sutcliffe, Heather L.
Probability
Primary 41A60, 60E05, 62E15, Secondary 33C10, 33C15, 33C45
Exact formulas are derived for the probability density functions of the sum and difference of two independent non-central gamma distributed random variables, with both series and integral representations of the density presented. These formulas are then applied to obtain asymptotic expansions for the probability density function, tail probabilities and quantile functions of these distributions. As a special case, we deduce asymptotic expansions for the probability density function of the product of correlated normal random variables with the coefficients given in closed-form. Numerical results are presented to assess the accuracy of our asymptotic approximations across a range of parameter constellations.
title The non-central gamma sum and difference distributions: exact distribution and asymptotic expansions
topic Probability
Primary 41A60, 60E05, 62E15, Secondary 33C10, 33C15, 33C45
url https://arxiv.org/abs/2605.15386