Videos

Connections Workshop: Extremal Combinatorics: Decomposing regular graphs into stars

February 7, 2025
Keywords:
  • extremal combinatorics
  • extremal set theory
  • extremal graph theory
  • hypergraphs
  • designs
  • Ramsey theory
  • positional games
  • random graphs
  • thresholds
  • probabilistic combinatorics
  • combinatorial probability
  • statistical physics
  • percolation
  • structural graph theory
  • graph minors
  • chromatic number
  • arithmetic combinatorics
  • arithmetic progressions
  • discrete geometry
  • combinatorial geometry
  • incidence theorems
MSC:
  • 05B05 - Combinatorial aspects of block designs [See also 51E05
  • 62K10]
  • 05B07 - Triple systems
  • 05C15 - Coloring of graphs and hypergraphs
  • 05C20 - Directed graphs (digraphs)
  • tournaments
  • 05C22 - Signed and weighted graphs
  • 05C25 - Graphs and abstract algebra (groups
  • rings
  • fields
  • etc.) [See also 20F65]
  • 05C35 - Extremal problems in graph theory [See also 90C35]
  • 05C50 - Graphs and linear algebra (matrices
  • eigenvalues
  • etc.)
  • 05C51 - Graph designs and isomorphic decomposition [See also 05B30]
  • 05C55 - Generalized Ramsey theory [See also 05D10]
  • 05C57 - Games on graphs (graph-theoretic aspects) [See also 91A43
  • 91A46]
  • 05C65 - Hypergraphs
  • 05C78 - Graph labelling (graceful graphs
  • bandwidth
  • 05C80 - Random graphs (graph-theoretic aspects) [See also 60B20]
  • 05C83 - Graph minors
  • 05D05 - Extremal set theory
  • 05D40 - Probabilistic methods in extremal combinatorics
  • including polynomial methods (combinatorial Nullstellensatz
  • 11B13 - Additive bases
  • including sumsets [See also 05B10]
  • 11B25 - Arithmetic progressions [See also 11N13]
  • 11B30 - Arithmetic combinatorics
  • higher degree uniformity
  • 11P70 - Inverse problems of additive number theory
  • including sumsets
  • 52C10 - ErdÅ‘s problems and related topics of discrete geometry [See also 11Hxx]
  • 52C30 - Planar arrangements of lines and pseudolines (aspects of discrete geometry)
  • 52C35 - Arrangements of points
  • flats
  • hyperplanes (aspects of discrete geometry) [See also 14N20
  • 32S22]
  • 60C05 - Combinatorial probability
Abstract
A $k$-star decomposition of a graph is a partition of the edge set into disjoint $k$-stars. Using the small subgraph conditioning method (SSCM), in 2018 Delcourt and Postle proved that with high probability, a random 4-regular graph has a 3-star decomposition. I will describe work to generalise this result. We have proved, again using the SSCM, that if a certain equation has a unique solution then with high probability, a random $d$-regular graphs has a $k$-star decomposition. We also prove that this sufficient condition holds whenever $k\leq d/2 + \log(d)/6$. There are connections with earlier work on beta-orientations which can be used to prove existence of $k$-star decompositions when $k \leq d/2$, while non-existence results can be obtained using a connection with independent sets in random regular graphs.