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Decidability of the Orbit Problem Over ℚ(X)
Abstract
The orbit problem is the problem of whether, given x, y∈ ℚn and an n× n matrix A, there exists an i∈ℕ such that Aix = y. In 1980, Kannan and Lipton proved that the orbit problem is decidable. We show that a generalization of the orbit problem, where the field is ℚ(X) for X a countable set of transcendentals, is also decidable. We define the orbit power problem for an arbitrary group G to be the problem of when, given x, y∈ G, there exists an n∈ℤ such that xn = y. We then use the main result to show that the power orbit problem is decidable for an assortment of groups, including the braid groups and Aut(F2).
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BibTeX
@misc{holden2026decidability,
title = {{Decidability of the Orbit Problem Over $\mathbbQ(X)$}},
author = {Joshua Holden and Alexa Renner},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.29440},
eprint = {2608.29440},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.29440},
}
RIS
TY - UNPB
TI - Decidability of the Orbit Problem Over ℚ(X)
AU - Joshua Holden
AU - Alexa Renner
PY - 2026
DA - 2026/08/29
PB - arXiv
DO - 10.48550/arxiv.2608.29440
UR - https://arxiv.org/abs/2608.29440
AB - The orbit problem is the problem of whether, given x, y∈ ℚ^n and an n× n matrix A, there exists an i∈ℕ such that A^ix = y. In 1980, Kannan and Lipton proved that the orbit problem is decidable. We show that a generalization of the orbit problem, where the field is ℚ(X) for X a countable set of transcendentals, is also decidable. We define the orbit power problem for an arbitrary group G to be the problem of when, given x, y∈ G, there exists an n∈ℤ such that x^n = y. We then use the main result to show that the power orbit problem is decidable for an assortment of groups, including the braid groups and Aut(F_2).
ER -