Concept

Degree distribution — where it appears

The share of a graph's vertices that have each number of neighbours. Two graphs with the same vertices and edges can distribute degree very differently, and costs set by the busiest vertices follow the distribution rather than the average degree.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

Also named here as orientation, preferential attachment, triangle counting — the same set of essays touches all of them, so they are one junction rather than several.

busiest vertexuniform pairsbusiest 16 · Σd² 43,104 · degeneracy 4attachmentbusiest 114 · Σd² 90,296 · degeneracy 4pairs of neighbours examineduniform pairs — every pair18,480uniform pairs — oriented4,090attachment — every pair42,076attachment — oriented3,339V = 1,024, E = 3,072 on both30 triangles and 249 — the answers, which also differ

Two parameters are not enough either

Two graphs on 1,024 vertices with 3,072 edges each — identical in both numbers every bound in this field is written in. Enumerating every pair of neighbours of every vertex costs 18,480 examinations on one and 42,076 on the other. The quantity that separates them is a third parameter, it is computable in linear time, and it appears in no statement of the problem.

graphs · Graph
ordered by degreedegeneracy orderthe degeneracy024681012largest out-degreeuniform pairs, degree 452 above duniform pairs, degree 6136 above duniform pairs, degree 1083 above dpreferential attachment, degree 414 above dpreferential attachment, degree 622 above dpreferential attachment, degree 1058 above d1,024 verticesdashed: the degeneracy

A bound right for the wrong reason

Orient every edge of a graph towards its higher-degree endpoint and count triangles among out-neighbours, and the work is O(E·d), where d is the graph's degeneracy. The usual reason given is that the orientation keeps every out-degree at most d. On a graph of 1,024 vertices with degeneracy four, 136 vertices have more than four out-neighbours and one has seven. The bound survives by a different argument, and the orientation that does keep every out-degree at most d does less work.

graphs · Graph

Named alongside it

The objects these essays reach for when they reach for this one.

Counted primitiveDegeneracyHonest limitMeasured countOrientationPreferential attachmentSparse graphTriangle countingComplexity classCounterexampleRegimeTwo parameter bound

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