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Track A: Algorithms, Complexity and Games

**Published in:** LIPIcs, Volume 297, 51st International Colloquium on Automata, Languages, and Programming (ICALP 2024)

A class of graphs admits an adjacency labeling scheme of size b(n), if the vertices in each of its n-vertex graphs can be assigned binary strings (called labels) of length b(n) so that the adjacency of two vertices can be determined solely from their labels.
We give bounds on the size of adjacency labels for every family of monotone (i.e., subgraph-closed) classes with a "well-behaved" growth function between 2^Ω(n log n) and 2^O(n^{2-δ}) for any δ > 0. Specifically, we show that for any function f: ℕ → ℝ satisfying log n ⩽ f(n) ⩽ n^{1-δ} for any fixed δ > 0, and some sub-multiplicativity condition, there are monotone graph classes with growth 2^O(nf(n)) that do not admit adjacency labels of size at most f(n) log n. On the other hand, any such class does admit adjacency labels of size O(f(n)log n). Surprisingly this bound is a Θ(log n) factor away from the information-theoretic bound of Ω(f(n)). Our bounds are tight upto constant factors, and the special case when f = log implies that the recently-refuted Implicit Graph Conjecture [Hatami and Hatami, FOCS 2022] also fails within monotone classes.
We further show that the Implicit Graph Conjecture holds for all monotone small classes. In other words, any monotone class with growth rate at most n! cⁿ for some constant c > 0, admits adjacency labels of information-theoretic order optimal size. In fact, we show a more general result that is of independent interest: any monotone small class of graphs has bounded degeneracy. We conjecture that the Implicit Graph Conjecture holds for all hereditary small classes.

Édouard Bonnet, Julien Duron, John Sylvester, Viktor Zamaraev, and Maksim Zhukovskii. Tight Bounds on Adjacency Labels for Monotone Graph Classes. In 51st International Colloquium on Automata, Languages, and Programming (ICALP 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 297, pp. 31:1-31:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{bonnet_et_al:LIPIcs.ICALP.2024.31, author = {Bonnet, \'{E}douard and Duron, Julien and Sylvester, John and Zamaraev, Viktor and Zhukovskii, Maksim}, title = {{Tight Bounds on Adjacency Labels for Monotone Graph Classes}}, booktitle = {51st International Colloquium on Automata, Languages, and Programming (ICALP 2024)}, pages = {31:1--31:20}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-322-5}, ISSN = {1868-8969}, year = {2024}, volume = {297}, editor = {Bringmann, Karl and Grohe, Martin and Puppis, Gabriele and Svensson, Ola}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2024.31}, URN = {urn:nbn:de:0030-drops-201741}, doi = {10.4230/LIPIcs.ICALP.2024.31}, annote = {Keywords: Adjacency labeling, degeneracy, monotone classes, small classes, factorial classes, implicit graph conjecture} }

Document

**Published in:** LIPIcs, Volume 274, 31st Annual European Symposium on Algorithms (ESA 2023)

We show that a canonical labeling of a random n-vertex graph can be obtained by assigning to each vertex x the triple (w₁(x),w₂(x),w₃(x)), where w_k(x) is the number of walks of length k starting from x. This takes time 𝒪(n²), where n² is the input size, by using just two matrix-vector multiplications. The linear-time canonization of a random graph is the classical result of Babai, Erdős, and Selkow. For this purpose they use the well-known combinatorial color refinement procedure, and we make a comparative analysis of the two algorithmic approaches.

Oleg Verbitsky and Maksim Zhukovskii. Canonization of a Random Graph by Two Matrix-Vector Multiplications. In 31st Annual European Symposium on Algorithms (ESA 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 274, pp. 100:1-100:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{verbitsky_et_al:LIPIcs.ESA.2023.100, author = {Verbitsky, Oleg and Zhukovskii, Maksim}, title = {{Canonization of a Random Graph by Two Matrix-Vector Multiplications}}, booktitle = {31st Annual European Symposium on Algorithms (ESA 2023)}, pages = {100:1--100:13}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-295-2}, ISSN = {1868-8969}, year = {2023}, volume = {274}, editor = {G{\o}rtz, Inge Li and Farach-Colton, Martin and Puglisi, Simon J. and Herman, Grzegorz}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2023.100}, URN = {urn:nbn:de:0030-drops-187536}, doi = {10.4230/LIPIcs.ESA.2023.100}, annote = {Keywords: Graph Isomorphism, canonical labeling, random graphs, walk matrix, color refinement, linear time} }

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**Published in:** LIPIcs, Volume 82, 26th EACSL Annual Conference on Computer Science Logic (CSL 2017)

Given a graph F, let I(F) be the class of graphs containing F
as an induced subgraph. Let W[F] denote the minimum k such that
I(F) is definable in k-variable first-order logic. The recognition
problem of I(F), known as Induced Subgraph Isomorphism (for the pattern graph F), is solvable in time O(n^{W[F]}). Motivated by this fact, we are interested in determining or estimating the value of W[F]. Using Olariu's characterization of paw-free graphs, we show that I(K_3+e) is definable by a first-order sentence of quantifier depth 3, where K_3+e denotes the paw graph. This provides an example of a graph F with W[F] strictly less than the number of vertices in F.
On the other hand, we prove that W[F]=4 for all F on 4 vertices
except the paw graph and its complement. If F is a graph on t vertices, we prove a general lower bound W[F]>(1/2-o(1))t, where the function in the little-o notation approaches 0 as t increases. This bound holds true even for a related parameter W^*[F], which is
defined as the minimum k such that I(F) is definable in the k-variable
infinitary logic. We show that W^*[F] can be strictly less than W[F]. Specifically, W^*[P_4]=3 for P_4 being the path graph on 4 vertices.

Oleg Verbitsky and Maksim Zhukovskii. On the First-Order Complexity of Induced Subgraph Isomorphism. In 26th EACSL Annual Conference on Computer Science Logic (CSL 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 82, pp. 40:1-40:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{verbitsky_et_al:LIPIcs.CSL.2017.40, author = {Verbitsky, Oleg and Zhukovskii, Maksim}, title = {{On the First-Order Complexity of Induced Subgraph Isomorphism}}, booktitle = {26th EACSL Annual Conference on Computer Science Logic (CSL 2017)}, pages = {40:1--40:16}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-045-3}, ISSN = {1868-8969}, year = {2017}, volume = {82}, editor = {Goranko, Valentin and Dam, Mads}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2017.40}, URN = {urn:nbn:de:0030-drops-76841}, doi = {10.4230/LIPIcs.CSL.2017.40}, annote = {Keywords: the induced subgraph isomorphism problem, descriptive and computational complexity, finite-variable first-order logic, quantifier depth and variable w} }

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