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Rigidity of graphs in homogeneous and locally homogeneous spaces
Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
2026 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Stelhet hos grafer i homogena och lokalt homogena rum (Swedish)
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 [en]
Rigidity, hypergraph, greedoid, Lie group, homogeneous space, symmetry, graph-of-groups
National Category
Geometry Discrete Mathematics Algebra and Logic
Research subject
Mathematics
Identifiers
URN: urn:nbn:se:umu:diva-253120ISBN: 978-91-6850-059-1 (electronic)ISBN: 978-91-6850-058-4 (print)OAI: oai:DiVA.org:umu-253120DiVA, id: diva2:2059777
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
List of papers
1. Structural rigidity and flexibility using graphs of groups
Open this publication in new window or tab >>Structural rigidity and flexibility using graphs of groups
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
Graph of groups, Hypergraph, Motion, Rigidity theory
National Category
Discrete Mathematics Computer Sciences
Identifiers
urn:nbn:se:umu:diva-249646 (URN)10.1007/s00200-025-00709-2 (DOI)001671691400001 ()2-s2.0-105028770661 (Scopus ID)
Funder
Wallenberg AI, Autonomous Systems and Software Program (WASP)Knut and Alice Wallenberg Foundation, 2020.0001
Available from: 2026-02-18 Created: 2026-02-18 Last updated: 2026-05-12
2. Sparsity greedoids and pebble game algorithms for posets
Open this publication in new window or tab >>Sparsity greedoids and pebble game algorithms for posets
(English)Manuscript (preprint) (Other academic)
National Category
Discrete Mathematics
Identifiers
urn:nbn:se:umu:diva-253118 (URN)
Available from: 2026-05-12 Created: 2026-05-12 Last updated: 2026-05-13Bibliographically approved
3. Hyperbolic symmetric rigidity and intrinsic surface geometry
Open this publication in new window or tab >>Hyperbolic symmetric rigidity and intrinsic surface geometry
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Mathematical sciences
Identifiers
urn:nbn:se:umu:diva-253115 (URN)
Available from: 2026-05-12 Created: 2026-05-12 Last updated: 2026-05-13Bibliographically approved
4. The rigidity of graphs in positive characteristic fields
Open this publication in new window or tab >>The rigidity of graphs in positive characteristic fields
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Mathematical sciences
Identifiers
urn:nbn:se:umu:diva-253114 (URN)
Available from: 2026-05-12 Created: 2026-05-12 Last updated: 2026-05-13Bibliographically approved
5. Homological methods in rigidity theory using graphs of groups
Open this publication in new window or tab >>Homological methods in rigidity theory using graphs of groups
(English)Manuscript (preprint) (Other academic)
National Category
Mathematical sciences
Research subject
Mathematics
Identifiers
urn:nbn:se:umu:diva-253109 (URN)
Available from: 2026-05-12 Created: 2026-05-12 Last updated: 2026-05-13Bibliographically approved

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Vermant, Joannes

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