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Title: The covariety of perfect numerical semigroups with fixed Frobenius number (English)
Author: Moreno-Frías, María Ángeles
Author: Rosales, José Carlos
Language: English
Journal: Czechoslovak Mathematical Journal
ISSN: 0011-4642 (print)
ISSN: 1572-9141 (online)
Volume: 74
Issue: 3
Year: 2024
Pages: 697-714
Summary lang: English
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Category: math
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Summary: Let $S$ be a numerical semigroup. We say that $h\in \mathbb {N} \backslash S$ is an isolated gap of $S$ if $\{h-1,h+1\}\subseteq S.$ A numerical semigroup without isolated gaps is called a perfect numerical semigroup. Denote by ${\rm m} (S)$ the multiplicity of a numerical semigroup $S$. A covariety is a nonempty family $\scr {C}$ of numerical semigroups that fulfills the following conditions: there exists the minimum of $\scr {C},$ the intersection of two elements of $\scr {C}$ is again an element of $\scr {C}$, and $S\backslash \{{\rm m}(S)\}\in \scr {C}$ for all $S\in \scr {C}$ such that $S\neq \min (\scr {C}).$ We prove that the set $\scr {P}(F)=\{S\colon S$ is a perfect numerical semigroup with Frobenius number $F\}$ is a covariety. Also, we describe three algorithms which compute: the set $\scr {P}(F),$ the maximal elements of $\scr {P}(F)$, and the elements of $\scr {P}(F)$ with a given genus. A ${\rm Parf}$-semigroup (or ${\rm Psat}$-semigroup) is a perfect numerical semigroup that in addition is an Arf numerical semigroup (or saturated numerical semigroup), respectively. We prove that the sets ${\rm Parf}(F)=\{S\colon S$ is a ${\rm Parf}$-numerical semigroup with Frobenius number $F\}$ and ${\rm Psat}(F)=\{S\colon S$ is a ${\rm Psat}$-numerical semigroup with Frobenius number $F\}$ are covarieties. As a consequence we present some algorithms to compute ${\rm Parf}(F)$ and ${\rm Psat}(F).$ (English)
Keyword: perfect numerical semigroup
Keyword: saturated numerical semigroup
Keyword: Arf numerical semigroup
Keyword: covariety
Keyword: Frobenius number
Keyword: genus
Keyword: algorithm
MSC: 11D07
MSC: 13H10
MSC: 20M14
DOI: 10.21136/CMJ.2024.0379-23
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Date available: 2024-10-03T12:34:00Z
Last updated: 2024-10-04
Stable URL: http://hdl.handle.net/10338.dmlcz/152576
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