Эта публикация цитируется в
3 статьях
Дискретная математика и математическая кибернетика
О максимальных графических разбиениях, ближайших к заданному графическому разбиению
В. А. Баранский,
Т. А. Сеньчонок Ural Federal University, 51, Lenina ave., Ekaterinburg, 620083, Russia
Аннотация:
A graphical partition is called
maximal if it is maximal under domination among graphical partitions of a given weight.
Let
$\lambda$ and
$\mu$ be partitions such that
$\mu\leq\lambda$. The
height of $\lambda$ over $\mu$ is the number of transformations in some shortest sequence of elementary transformations which transforms
$\lambda$ to
$\mu$, denoted by
$\mathrm{height}(\lambda,\mu)$. For a given graphical partition
$\mu$, a maximal graphical partition
$\lambda$ such that
$\mu\leq\lambda$ and
$\mathrm{sum}(\mu)= \mathrm{sum}(\lambda)$ is called the
$h$-
nearest to
$\mu$ if it has the minimal height over
$\mu$ among all maximal graphical partitions
$\lambda'$ such that
$\mu\leq\lambda'$ and
$\mathrm{sum}(\mu)= \mathrm{sum}(\lambda')$. The aim is to prove the following result:
Let
$\mu$ be a graphical partition and
$\lambda$ be an
$h$-nearest maximal graphical partition to
$\mu$. Then
- either $r(\lambda)=r(\mu)-1$, $l(\mathrm{tl}(\mu))<r(\mu)$ or $r(\lambda)=r(\mu)$,
- $\mathrm{height}(\lambda,\mu)= \mathrm{height}(\mathrm{tl}(\mu), \mathrm{hd}(\mu))- \frac{1}{2}[\mathrm{sum}(\mathrm{tl}(\mu))-\mathrm{sum}(\mathrm{hd}(\mu))]= \frac{1}{2}\sum^r_{i=1}|\mathrm{tl}(\mu)_i-\mathrm{hd}(\mu)_i|,$
where
$r=r(\mu)$ is the rank,
$\mathrm{hd}(\mu))$ is the head and
$\mathrm{tl}(\mu))$ is the tail of the partition
$\mu$,
$l(\mathrm{tl}(\mu))$ is the length of
$\mathrm{tl}(\mu)$.
We provide an algorithm that generates some
$h$-nearest to
$\mu$ maximal graphical partition
$\lambda$ such that
$r(\lambda)=r(\mu)$. For the case
$l(\mathrm{tl}(\mu))<r(\mu)$, we also provide an algorithm that generates some
$h$-nearest to
$\mu$ maximal graphical partition
$\lambda$ such that
$r(\lambda)=r(\mu)-1$.
In addition we present a new proof of the Kohnert's criterion for a partition to be graphical not using other criteria.
Ключевые слова:
threshold graphs, lattice of integer partitions, graphical partition, maximal graphical partition, Ferrer's diagram.
УДК:
519.165
MSC: 05A17 Поступила 9 ноября 2019 г., опубликована
10 марта 2020 г.
DOI:
10.33048/semi.2020.17.022