Deformation spaces of $G$-trees and automorphisms of Baumslag–Solitar groups
Author(s) -
Matt Clay
Publication year - 2009
Publication title -
groups geometry and dynamics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 25
eISSN - 1661-7215
pISSN - 1661-7207
DOI - 10.4171/ggd/51
Subject(s) - automorphism , mathematics , computation , finitely generated abelian group , algebraic number , invariant (physics) , pure mathematics , automorphism group , combinatorics , mathematical analysis , algorithm , mathematical physics
We construct an invariant deformation retract of a deformation space ofG-trees. We show that this complex is finite dimensional in certain cases andprovide an example that is not finite dimensional. Using this complex wecompute the automorphism group of the classical non-solvable Baumslag-Solitargroups BS(p,q). The most interesting case is when p properly divides q. Collinsand Levin computed a presentation for Aut(BS(p,q)) in this case using algebraicmethods. Our computation uses Bass-Serre theory to derive these presentations.Additionally, we provide a geometric argument showing Out(BS(p,q)) is notfinitely generated when p properly divides q.
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