On positivity of orthogonal series and its applications in probability

Autor: Szabłowski, Paweł J.
Rok vydání: 2020
Předmět:
Zdroj: Positivity 26, Aricle number 19(2022)
Druh dokumentu: Working Paper
DOI: 10.1007/s11117-022-00883-4
Popis: We give necessary and sufficient conditions for an orthogonal series to converge in the mean-squares to a nonnegative function. We present many examples and applications, in analysis and probability. In particular, we give necessary and sufficient conditions for a Lancaster-type of expansion $% \sum_{n\geq 0}c_{n}\alpha _{n}(x)\beta _{n}(y)$ with two sets of orthogonal polynomials $\left\{ \alpha _{n}\right\} $ and $\left\{ \beta _{n}\right\} $ to converge in means-squares to a nonnegative bivariate function. In particular, we study the properties of the set $C(\alpha ,\beta )$ of the sequences $\left\{ c_{n}\right\} ,$ for which the above-mentioned series converge to a nonnegative function and give conditions for the membership to it. Further we show that the class of bivariate distributions for which a Lancaster type expansion can be found, is the same as the class of distributions having all conditional moments in the form of polynomials in the conditioning random variable.
Comment: 17
Databáze: arXiv
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