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Structural rigidity and flexibility using graphs of groups
Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.ORCID iD: 0000-0002-5040-2089
Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
2026 (English)In: Applicable Algebra in Engineering, Communication and Computing, ISSN 0938-1279, E-ISSN 1432-0622Article in journal (Refereed) Epub ahead of print
Abstract [en]

In structural rigidity, one studies frameworks of bars and joints in Euclidean space. Such a framework is an articulated structure consisting of rigid bars joined together at joints around which the bars may rotate. In this paper, we will describe articulated motions of realisations of hypergraphs that uses the terminology of graph of groups, and describe the motions of such a framework using group theory. Our approach allows to model a variety of situations, such as parallel redrawings, scenes, polytopes, realisations of graphs on surfaces, and even unique colourability of graphs. This approach allows a concise description of various dualities in rigidity theory. We also provide a lower bound on the dimension of the infinitesimal motions of such a framework in the special case when the underlying group is a Lie group.

Place, publisher, year, edition, pages
Springer, 2026.
Keywords [en]
Graph of groups, Hypergraph, Motion, Rigidity theory
National Category
Discrete Mathematics Computer Sciences
Identifiers
URN: urn:nbn:se:umu:diva-249646DOI: 10.1007/s00200-025-00709-2ISI: 001671691400001Scopus ID: 2-s2.0-105028770661OAI: oai:DiVA.org:umu-249646DiVA, id: diva2:2039652
Funder
Wallenberg AI, Autonomous Systems and Software Program (WASP)Knut and Alice Wallenberg Foundation, 2020.0001Available from: 2026-02-18 Created: 2026-02-18 Last updated: 2026-05-12
In thesis
1. Rigidity of graphs in homogeneous and locally homogeneous spaces
Open this publication in new window or tab >>Rigidity of graphs in homogeneous and locally homogeneous spaces
2026 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Stelhet hos grafer i homogena och lokalt homogena rum
Abstract [en]

This thesis studies rigidity of graphs and hypergraphs realised in homogeneous and locally homogeneous spaces. We develop an algebraic model for describing the motions of such realisations using group-theoretic methods. The resulting structures, which we call graph-of-groups realisations, provide a unified model capable of capturing a wide range of rigidity problems. Within this model, we recover foundational results, including a necessary condition for rigidity. Using homological methods, we show that, generically, this condition is also sufficient for rigidity problems in homogeneous spaces G/H, where H is a one-dimensional and selfnormalising subgroup of a Lie group G. The resulting combinatorial conditions can be verified using the pebble game algorithm, which we analyse in novel settings. Beyond homogeneous spaces, we also study realisations of graphs in locally homogeneous spaces by interpreting these graphs as symmetric graphs in a homogeneous space. In particular, we study the minimal rigidity of symmetric graphs in the hyperbolic plane and obtain a combinatorial characterisation of minimal rigidity of graphs realised on compact orientable surfaces of genus g≥2.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2026. p. 39
Series
Doctoral thesis / Umeå University, Department of Mathematics, ISSN 1102-8300
Keywords
Rigidity, hypergraph, greedoid, Lie group, homogeneous space, symmetry, graph-of-groups
National Category
Geometry Discrete Mathematics Algebra and Logic
Research subject
Mathematics
Identifiers
urn:nbn:se:umu:diva-253120 (URN)978-91-6850-059-1 (ISBN)978-91-6850-058-4 (ISBN)
Public defence
2026-06-09, Lindellhallen 3, Universitetstorget 16, Umeå 907 36, 09:00 (English)
Opponent
Supervisors
Available from: 2026-05-19 Created: 2026-05-12 Last updated: 2026-05-13Bibliographically approved

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Stokes, KlaraVermant, Joannes

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