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JOURNALS // Vestnik Udmurtskogo Universiteta. Matematika. Mekhanika. Komp'yuternye Nauki // Archive

Vestn. Udmurtsk. Univ. Mat. Mekh. Komp. Nauki, 2013 Issue 4, Pages 3–12 (Mi vuu396)

This article is cited in 6 papers

MATHEMATICS

The graph of partial orders

Kh. Sh. Al' Dzhabri, V. I. Rodionov

Udmurt State University, ul. Universitetskaya, 1, Izhevsk, 426034, Russia

Abstract: Any binary relation $\sigma\subseteq X^2$ (where $X$ is an arbitrary set) generates a characteristic function on the set $X^2$: if $(x,y)\in\sigma$, then $\sigma(x,y)=1$, otherwise $\sigma(x,y)=0$. In terms of characteristic functions on the set of all binary relations of the set $X$ we introduced the concept of a binary reflexive relation of adjacency and determined the algebraic system consisting of all binary relations of a set and of all unordered pairs of various adjacent binary relations. If $X$ is finite set then this algebraic system is a graph (“a graph of graphs”).
It is shown that if $\sigma$ and $\tau$ are adjacent relations then $\sigma$ is a partial order if and only if $\tau$ is a partial order. We investigated some features of the structure of the graph $G(X)$ of partial orders. In particular, if $X$ consists of $n$ elements, and $T_0(n)$ is the number of labeled $T_0$-topologies defined on the set $X$, then the number of vertices in a graph $G(X)$ is $T_0(n)$, and the number of connected components is $T_0(n-1)$.
For any partial order $\sigma$ there is defined the notion of its support set $S(\sigma)$, which is some subset of $X$. If $X$ is finite set, and partial orders $\sigma$ and $\tau$ belong to the same connected component of the graph $G(X)$, then the equality $S(\sigma)=S(\tau)$ holds if and only if $\sigma=\tau$. It is shown that in each connected component of the graph $G(X)$ the union of support sets of its elements is a specific partially ordered set with respect to natural inclusion relation of sets.

Keywords: binary relation, graph, partial order, finite topology.

UDC: 519.175+519.115.5

MSC: 05C30

Received: 13.08.2013



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