English

The exact power law and Pascal pyramid

Probability 2017-05-12 v1 Combinatorics

Abstract

Let ω0,ω1,,ωn\omega_0, \omega_1,\ldots, \omega_n be a full set of outcomes (letters, symbols) and let positive pip_i, i=0,,ni=0,\ldots,n, be their probabilities (i=0npi=1\sum_{i=0}^n p_i=1). Let us treat ω0\omega_0 as a stop symbol; it can occur in sequences of symbols (we call them words) only once, at the very end. The probability of a word is defined as the product of probabilities of its letters. We consider the list of all possible words sorted in the non-increasing order of their probabilities. Let p(r)p(r) be the probability of the rrth word in this list. We prove that if at least one of ratios logpi/logpj\log p_i/\log p_j, i,j{1,,n}i,j\in\{ 1,\ldots,n\}, is irrational, then the limit limrp(r)/r1/γ\lim_{r\to\infty} p(r)/r^{1/\gamma} exists and differs from zero; here γ\gamma is the root of the equation i=1npiγ=1\sum_{i=1}^n p_i^\gamma=1. Some weaker results were established earlier. We are first to write an explicit formula for this limit constant at the power function; it can be expressed (rather easily) in terms of the entropy of the distribution~(p1γ,,pnγ)(p_1^\gamma,\ldots,p_n^\gamma).

Keywords

Cite

@article{arxiv.1605.09052,
  title  = {The exact power law and Pascal pyramid},
  author = {Vladimir V. Bochkarev and Eduard Yu. Lerner},
  journal= {arXiv preprint arXiv:1605.09052},
  year   = {2017}
}

Comments

19 pages

R2 v1 2026-06-22T14:12:27.574Z