Combinatorial problems - a place where classical enumeration fails | Pavol Kollár

Combinatorial problems - a place where classical enumeration fails | Pavol Kollár

🎙 Pavol Kollár 👥 1K 📅 May 7, 2026 ⏱ 35 min 👁 85 📄 lecture 🧭 2026-08-15
Available in: English (current) Français

Keywords

graph automorphismvertex-transitive graphCayley graphr-regular familyboundary matricesanti-dictionary languagedynamic programmingtransition graphde Bruijn graph

Summary

The lecture by Pavol Kollár, a third-year student, presents two combinatorial problems where classical enumeration fails. The first problem concerns r-regular families of permutations, generalizing Cayley graphs. The speaker explains the concept of vertex-transitive graphs and Cayley graphs, then introduces r-regular families as a generalization, referencing work by Janet Goyak, Robert and Gareth Jones, and Philip Carrick. He describes his own computational approach using Fourier transforms and matrix representations to estimate the number of r-regular families on five elements, which is on the order of 10^24. The second problem involves enumerating binary matrices avoiding forbidden submatrices, called boundary matrices. He connects this to anti-dictionary languages and uses dynamic programming and transition graphs to count them. He proves a theorem about the growth of the number of boundary matrices based on the structure of the transition graph, and discusses the existence of a single linear recurrence for the whole table. The talk concludes with future directions and ongoing computations on a cluster.

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Critical Evaluation

Value of the Information & Strength of the Argument

The talk provides valuable insights into advanced combinatorial enumeration problems. The speaker clearly explains the motivation and the mathematical background, and presents his own contributions, including a computational algorithm and a theorem about boundary matrices. The argumentation is solid, with references to prior work and logical reasoning. However, some parts are presented as ongoing work without complete proofs, which is acceptable for a lecture but limits the depth of the argumentation.

Scientific Rigor, Source Quality, Title Accuracy

The speaker references several papers, including those by Janet Goyak, Robert and Gareth Jones, and the trio Yaiti, Yates, and Opal. He also mentions his own paper in preparation. The sources are relevant and well-integrated. The title accurately reflects the content, focusing on combinatorial problems where classical enumeration fails. The talk is well-structured and the mathematical rigor is high, though the presentation is at a level suitable for an academic audience.

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Title / Content Match

The title accurately reflects the content, which focuses on combinatorial enumeration problems where classical methods fail, and presents alternative approaches.

Quality & Reliability

7/10

The talk presents original research in combinatorics, with references to established papers and ongoing computational work. The speaker is a student, but the content is rigorous and well-structured. Some claims are not fully detailed due to time constraints, but the methodology is sound.

Key Moments

Cited Sources

  • Goyak, J. (1996). Quasi-groups and graph automorphisms. — Mentioned as the origin of the concept of quasi-groups and r-regular families.
  • Yaiti, R., & Jones, G. (year unknown). Paper on r-regular families. — Mentioned as the first generalization of Cayley graphs to r-regular families.
  • Carrick, P. (bachelor thesis). Generation of r-regular families. — Mentioned as using computer power to generate lists of r-regular families.
  • Yaiti, R., Yates, & Opal (2018). Paper on boundary matrices. — Mentioned as revisiting dynamic programming for boundary matrices.

Concurring Sources

  • Yaiti, R., & Jones, G. (year unknown). Paper on r-regular families. — The speaker's work builds on this paper, and the results are consistent with it.
  • Yaiti, R., Yates, & Opal (2018). Paper on boundary matrices. — The speaker's dynamic programming approach is based on this paper, and his theorem extends it.

Dissenting Sources

  • None — No discordant sources were mentioned in the talk.

Contribution & Novelties

The talk presents original research in two areas: estimating the number of r-regular families using Fourier transforms and matrix representations, and proving a theorem about the growth of boundary matrices based on transition graph structure. The speaker also proposes a ‘one recurrence to rule them all’ for boundary matrices, which is a novel idea.

Pour aller plus loin :

97 words

Radar Profile

The radar profile shows high scores in quantity and quality of information, and technical level, reflecting the advanced mathematical content. The reliability score is slightly lower due to the ongoing nature of the research and the lack of complete proofs in the presentation.

Reliability 7/10