Ascents of Size Less Than \(d\) in Samples of Geometric Random Variables: Mean, Variance, and Distribution

Charlotte Brennan1
1THE JOHN KNOPFMACHER CENTRE FOR APPLICABLE ANALYSIS AND NuMBER THEORY, SCHOOL OF MATHEMATICS, UNIVERSITY OF THE WITWATERSRAND, PrivaTE BAG 3, Wits 2050, JOHANNESBURG, SOUTH AFRICA

Abstract

We consider words \(\pi_1\pi_2\pi_3\ldots\pi_n\) of length \(n\), where \(\pi_i \in \mathbb{N}\) are independently generated with a geometric probability

\[P({\pi} = k) = p(q)^{k-1} \text{where p + q = 1}. \]

Let \(d\) be a fixed non-negative integer. We say that we have an ascent of size \(d\) or more, an ascent of size less than \(d\), a level, and a descent if \({\pi}_{i+1} \geq {\pi}_i+d \), \({\pi}_{i+1} {\pi}_{i+1} \), respectively.We determine the mean and variance of the number of ascents of size less than \(d\) in a random geometrically distributed word. We also show that the distribution is Gaussian as \(n\) tends to infinity.