Maximizing the Probability of Fixation in the Positional Voter Model

Research output: Contribution to book/anthology/report/proceedingArticle in proceedingsResearchpeer-review


The Voter model is a well-studied stochastic process that models the invasion of a novel trait A (e.g., a new opinion, social meme, genetic mutation, magnetic spin) in a network of individuals (agents, people, genes, particles) carrying an existing resident trait B. Individuals change traits by occasionally sampling the trait of a neighbor, while an invasion bias δ ≥ 0 expresses the stochastic preference to adopt the novel trait A over the resident trait B. The strength of an invasion is measured by the probability that eventually the whole population adopts trait A, i.e., the fixation probability. In more realistic settings, however, the invasion bias is not ubiquitous, but rather manifested only in parts of the network. For instance, when modeling the spread of a social trait, the invasion bias represents localized incentives. In this paper, we generalize the standard biased Voter model to the positional Voter model, in which the invasion bias is effectuated only on an arbitrary subset of the network nodes, called biased nodes. We study the ensuing optimization problem, which is, given a budget k, to choose k biased nodes so as to maximize the fixation probability of a randomly occurring invasion. We show that the problem is NP-hard both for finite δ and when δ → ∞ (strong bias), while the objective function is not submodular in either setting, indicating strong computational hardness. On the other hand, we show that, when δ → 0 (weak bias), we can obtain a tight approximation in O(n) time, where ω is the matrix-multiplication exponent. We complement our theoretical results with an experimental evaluation of some proposed heuristics.

Original languageEnglish
Title of host publicationAAAI-23 Technical Tracks 10
EditorsBrian Williams, Yiling Chen, Jennifer Neville
Number of pages9
PublisherAAAI Press
Publication date27 Jun 2023
Article number190493
ISBN (Electronic)9781577358800
Publication statusPublished - 27 Jun 2023
Event37th AAAI Conference on Artificial Intelligence, AAAI 2023 - Washington, United States
Duration: 7 Feb 202314 Feb 2023


Conference37th AAAI Conference on Artificial Intelligence, AAAI 2023
Country/TerritoryUnited States
SponsorAssociation for the Advancement of Artificial Intelligence
SeriesProceedings of the 37th AAAI Conference on Artificial Intelligence, AAAI 2023


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