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We present an algorithm for simulating a distribution using prefix conditional samples (Adar, Fischer and Levi, 2024), as well as "prefix-compatible" conditional models such as the interval model (Cannone, Ron and Servedio, 2015) and the subcube model (CRS15, Bhattacharyya and Chakraborty, 2018). The sample complexity is O(log² N/ε²) prefix conditional samples per query, which improves on the previously known Õ(log³ N/ε²) (Kumar, Meel and Pote, 2025). Moreover, our simulating distribution is O(ε²)-close to the input distribution with respect to the Kullback-Leibler divergence, which is stricter than the usual guarantee of being O(ε)-close with respect to the total-variation distance. We show that our algorithm is tight with respect to the highly-related task of estimation: every algorithm that is able to estimate the mass of individual elements within (1 ± ε)-multiplicative error must make Ω(log²N/ε²) prefix conditional samples per element.
@InProceedings{adar:LIPIcs.APPROX/RANDOM.2026.32,
author = {Adar, Tomer},
title = {{Tight Simulation of a Distribution Using Conditional Samples}},
booktitle = {Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques (APPROX/RANDOM 2026)},
pages = {32:1--32:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-449-9},
ISSN = {1868-8969},
year = {2026},
volume = {392},
editor = {Singh, Mohit and Gur, Tom},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.APPROX/RANDOM.2026.32},
URN = {urn:nbn:de:0030-drops-277496},
doi = {10.4230/LIPIcs.APPROX/RANDOM.2026.32},
annote = {Keywords: Distribution learning, Distribution simulation, Probability estimation}
}