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  • Jonsson, Jakob,1972-KTH,Matematik (Avd.) (author)

Simplicial Complexes of Graphs

  • BookEnglish2005

Publisher, publication year, extent ...

  • Stockholm :KTH,2005
  • xiii, 350 s.
  • electronicrdacarrier

Numbers

  • LIBRIS-ID:oai:DiVA.org:kth-202
  • ISBN:9171780483
  • https://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-202URI

Supplementary language notes

  • Language:English
  • Summary in:English

Part of subdatabase

Classification

  • Subject category:vet swepub-contenttype
  • Subject category:dok swepub-publicationtype

Series

  • Trita-MAT. MA,1401-2278 ;05:07

Notes

  • QC 20100622
  • Let G be a finite graph with vertex set V and edge set E. A graph complex on G is an abstract simplicial complex consisting of subsets of E. In particular, we may interpret such a complex as a family of subgraphs of G. The subject of this thesis is the topology of graph complexes, the emphasis being placed on homology, homotopy type, connectivity degree, Cohen-Macaulayness, and Euler characteristic. We are particularly interested in the case that G is the complete graph on V. Monotone graph properties are complexes on such a graph satisfying the additional condition that they are invariant under permutations of V. Some well-studied monotone graph properties that we discuss in this thesis are complexes of matchings, forests, bipartite graphs, disconnected graphs, and not 2-connected graphs. We present new results about several other monotone graph properties, including complexes of not 3-connected graphs and graphs not coverable by p vertices. Imagining the vertices as the corners of a regular polygon, we obtain another important class consisting of those graph complexes that are invariant under the natural action of the dihedral group on this polygon. The most famous example is the associahedron, whose faces are graphs without crossings inside the polygon. Restricting to matchings, forests, or bipartite graphs, we obtain other interesting complexes of noncrossing graphs. We also examine a certain "dihedral" variant of connectivity. The third class to be examined is the class of digraph complexes. Some well-studied examples are complexes of acyclic digraphs and not strongly connected digraphs. We present new results about a few other digraph complexes, including complexes of graded digraphs and non-spanning digraphs. Many of our proofs are based on Robin Forman's discrete version of Morse theory. As a byproduct, this thesis provides a loosely defined toolbox for attacking problems in topological combinatorics via discrete Morse theory. In terms of simplicity and power, arguably the most efficient tool is Forman's divide and conquer approach via decision trees, which we successfully apply to a large number of graph and digraph complexes.

Subject headings and genre

  • NATURVETENSKAP Matematik hsv//swe
  • NATURAL SCIENCES Mathematics hsv//eng
  • Algebra and geometry
  • simplicial complex
  • monotone graph property
  • discrete Morse theory
  • simplicial homology
  • homotopy type
  • connectivity degree
  • Cohen-Macaulay complex
  • Euler characteristic
  • decision tree
  • Algebra och geometri
  • Algebra and geometry
  • Algebra och geometri

Added entries (persons, corporate bodies, meetings, titles ...)

  • Björner, AndersKTH,Matematik (Inst.) (thesis advisor)
  • Shareshian, JohnDepartment of Mathematics, Washington University, St. Louis, MO (opponent)
  • KTHMatematik (Avd.) (creator_code:org_t)

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By the author/editor
Jonsson, Jakob, ...
Björner, Anders
Shareshian, John
About the subject
NATURAL SCIENCES
NATURAL SCIENCES
and Mathematics
Parts in the series
Trita-MAT. MA,
By the university
Royal Institute of Technology

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