Optimal support and condensation in random allocations
Abstract
How many distinct symbols should a password use? If its length is fixed at n and an observer learns only which symbols appear, the number of compatible passwords is maximized asymptotically when k/n→1/(2log2). We ask what changes when, in addition to the length, aggregate information about the repetition pattern is revealed. We model this by fixing a second additive profile Vk=∑i v(Ji) at scale Vk/n≈ρ. For v(j)=log(j!), the profile records the reduction in the logarithm of the number of compatible words caused by repetitions; we show that once the normalized profile ρ exceeds 0.507834…, the limiting optimal fraction is pinned at 1/2. For a typical multiplicity profile at the optimal support above this threshold, the excess in Vk is carried by a vanishing fraction of used symbols. We interpret this as a form of non-equivalence of ensembles and extend the mechanism to other profiles and non-uniform allocation models.
Related
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BibTeX
@misc{ottolini2026optimal,
title = {{Optimal support and condensation in random allocations}},
author = {Andrea Ottolini},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.24848},
eprint = {2609.24848},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.24848},
}
RIS
TY - UNPB
TI - Optimal support and condensation in random allocations
AU - Andrea Ottolini
PY - 2026
DA - 2026/09/21
PB - arXiv
DO - 10.48550/arxiv.2609.24848
UR - https://arxiv.org/abs/2609.24848
AB - How many distinct symbols should a password use? If its length is fixed at n and an observer learns only which symbols appear, the number of compatible passwords is maximized asymptotically when k/n→1/(2log2). We ask what changes when, in addition to the length, aggregate information about the repetition pattern is revealed. We model this by fixing a second additive profile V_k=∑_i v(J_i) at scale V_k/n≈ρ. For v(j)=log(j!), the profile records the reduction in the logarithm of the number of compatible words caused by repetitions; we show that once the normalized profile ρ exceeds 0.507834…, the limiting optimal fraction is pinned at 1/2. For a typical multiplicity profile at the optimal support above this threshold, the excess in V_k is carried by a vanishing fraction of used symbols. We interpret this as a form of non-equivalence of ensembles and extend the mechanism to other profiles and non-uniform allocation models.
ER -