Complex Representatives, Similarity Invariants, and Iterates in bfU(1,1;ℍ)
Abstract
We study the similarity classes of matrices in U(1,1;ℍ) and the iterates of their associated quaternionic Möbius transformations. Building on the known elliptic case, we show that every parabolic or loxodromic element of U(1,1;ℍ) is similar, via a matrix in U(1,1;ℍ), to a complex matrix. Explicit complex representatives and matrices realizing these similarities are constructed for the different types. We then introduce the invariants Tr(T), Δ(T), η(T), κ(T), and prove that they form a complete system of similarity invariants for matrices in U(1,1;ℍ). Finally, using the complex representation of quaternionic matrices and Chebyshev polynomials, we derive a fourth-order recurrence for a real sequence (qn) satisfying Δ(Tn)=qn2Δ(T). Together with recurrence relations for the relevant matrix entries, this identity yields a complete classification of the quaternionic Möbius transformation associated with Tn, including the degenerate cases in which Δ(Tn)=0.
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BibTeX
@misc{hou2026complex,
title = {{Complex Representatives, Similarity Invariants, and Iterates in $\bfU(1,1;\mathbbH)$}},
author = {Bingzhe Hou and Cailing Yao and Jiaxing He},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.24580},
eprint = {2610.24580},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.24580},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Complex Representatives, Similarity Invariants, and Iterates in bfU(1,1;ℍ)
AU - Bingzhe Hou
AU - Cailing Yao
AU - Jiaxing He
PY - 2026
DA - 2026/10/17
PB - arXiv
DO - 10.48550/arxiv.2610.24580
UR - https://arxiv.org/abs/2610.24580
AB - We study the similarity classes of matrices in U(1,1;ℍ) and the iterates of their associated quaternionic Möbius transformations. Building on the known elliptic case, we show that every parabolic or loxodromic element of U(1,1;ℍ) is similar, via a matrix in U(1,1;ℍ), to a complex matrix. Explicit complex representatives and matrices realizing these similarities are constructed for the different types. We then introduce the invariants Tr(T), Δ(T), η(T), κ(T), and prove that they form a complete system of similarity invariants for matrices in U(1,1;ℍ). Finally, using the complex representation of quaternionic matrices and Chebyshev polynomials, we derive a fourth-order recurrence for a real sequence (q_n) satisfying Δ(T^n)=q_n^2Δ(T). Together with recurrence relations for the relevant matrix entries, this identity yields a complete classification of the quaternionic Möbius transformation associated with T^n, including the degenerate cases in which Δ(T^n)=0.
ER -