| 研究課題/領域番号 |
19K11815
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| 研究種目 |
基盤研究(C)
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| 配分区分 | 基金 |
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| 応募区分 | 一般 |
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| 審査区分 |
小区分60010:情報学基礎論関連
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| 研究機関 | 秋田大学 |
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研究代表者 |
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| 研究期間 (年度) |
2019-04-01 – 2024-03-31
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| 研究課題ステータス |
完了 (2023年度)
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| 配分額 *注記 |
4,030千円 (直接経費: 3,100千円、間接経費: 930千円)
2021年度: 1,430千円 (直接経費: 1,100千円、間接経費: 330千円)
2020年度: 1,300千円 (直接経費: 1,000千円、間接経費: 300千円)
2019年度: 1,300千円 (直接経費: 1,000千円、間接経費: 300千円)
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| キーワード | repetitions in strings / distinct squares / upper bound / combinatorics on words / stringology / repetitions / squares / upper bounds / square network / distinguished positions / Repetitions / Squares / Combinatorics on words / Distinct repetitions |
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| 研究開始時の研究の概要 |
The main questions in this research project are: how many repetition occurrences and how many unique repetition types (distinct repetitions) can there be in a word (sequence)? I aim to improve existing bounds for distinct repetitions, in particular, tackling a famous conjecture by Fraenkel and Simpson on the number of squares. I propose a fresh approach to understand the structure of distinct repetitions through clusters of their roots, which is expected to lead to improvements in the bounds and provide an easy, visually informative way of presenting their proofs.
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| 研究実績の概要 |
In the final year of the grant we worked on the extension of Brlek and Li's result concerning the upper bound on distinct repetitions in strings. They proved the upper bound equal to the length of the string divided by the exponent minus one, using an approach with Rauzy graphs.
We managed to extend the approach to prove our conjecture regarding the clusters of distinct repetition roots: the cluster of each root U is strictly larger than the number of distinct repetition roots that have U as a prefix. This is a stronger result, which implies the upper bound on the number of distinct repetitions proved by Brlek and Li. The method used is an extension of the Rauzy graph approach, introducing x-prefixed Rauzy graphs for each distinct root x.
The manuscript with the final results is in preparation.
Our result will open up new directions for investigating repetitions in strings by considering the nested cluster structures of the repetition roots, and studying what structures allow for high repetition density in the strings. We showed earlier that our lower bound on cluster sizes is optimal when the roots are linearly ordered by the prefix relation. An interesting question to pursue is whether the lower bound is optimal when the roots form a non-linear partial order under the prefix relation.
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