scholarly journals The MacNeille Completion of the Poset of Partial Injective Functions

10.37236/786 ◽  
2008 ◽  
Vol 15 (1) ◽  
Author(s):  
Marc Fortin
Keyword(s):  
Symmetric Group ◽  
Bruhat Order ◽  
Natural Order ◽  
Macneille Completion ◽  
Alternating Sign Matrices ◽  
Irreducible Elements ◽  
Increasing Functions

Renner has defined an order on the set of partial injective functions from $[n]=\{1,\ldots,n\}$ to $[n]$. This order extends the Bruhat order on the symmetric group. The poset $P_{n}$ obtained is isomorphic to a set of square matrices of size $n$ with its natural order. We give the smallest lattice that contains $P_{n}$. This lattice is in bijection with the set of alternating matrices. These matrices generalize the classical alternating sign matrices. The set of join-irreducible elements of $P_{n}$ are increasing functions for which the domain and the image are intervals.

scholarly journals Posets of Finite Functions

10.37236/5272 ◽  
2016 ◽  
Vol 23 (1) ◽  
Author(s):  
Konrad Pióro
Keyword(s):  
Symmetric Group ◽  
Linear Algebra ◽  
Bruhat Order ◽  
Negative Integer ◽  
Macneille Completion ◽  
Partial Functions ◽  
Matrix Representations ◽  
Partially Ordered ◽  
Irreducible Elements ◽  
Algebraic Monoids

The symmetric group $ S(n) $ is partially ordered by Bruhat order. This order is extended by L. Renner to the set of partial injective functions of $ \{ 1, 2, \ldots, n \} $ (see, Linear Algebraic Monoids, Springer, 2005). This poset is investigated by M. Fortin in his paper The MacNeille Completion of the Poset of Partial Injective Functions [Electron. J. Combin., 15, R62, 2008]. In this paper we show that Renner order can be also defined for sets of all functions, partial functions, injective and partial injective functions from $ \{ 1, 2, \ldots, n \} $ to $ \{ 1, 2, \ldots, m \} $. Next, we generalize Fortin's results on these posets, and also, using simple facts and methods of linear algebra, we give simpler and shorter proofs of some fundamental Fortin's results. We first show that these four posets can be order embedded in the set of $ n \times m $-matrices with non-negative integer entries and with the natural componentwise order. Second, matrix representations of the Dedekind-MacNeille completions of our posets are given. Third, we find join- and meet-irreducible elements for every finite sublattice of the lattice of all $ n \times m $-matrices with integer entries. In particular, we obtain join- and meet-irreducible elements of these Dedekind-MacNeille completions. Hence and by general results concerning Dedekind-MacNeille completions, join- and meet-irreducible elements of our four posets of functions are also found. Moreover, subposets induced by these irreducible elements are precisely described.

scholarly journals Intervals and factors in the Bruhat order

2015 ◽  
Vol Vol. 17 no. 1 (Combinatorics) ◽  
Author(s):  
Bridget Eileen Tenner
Keyword(s):  
Symmetric Group ◽  
Bruhat Order ◽  
Order Ideal ◽  
Principal Order ◽  
International Audience ◽  
Reduced Words

Combinatorics International audience In this paper we study those generic intervals in the Bruhat order of the symmetric group that are isomorphic to the principal order ideal of a permutation w, and consider when the minimum and maximum elements of those intervals are related by a certain property of their reduced words. We show that the property does not hold when w is a decomposable permutation, and that the property always holds when w is the longest permutation.

scholarly journals IRREDUCIBLE QUASIORDERS OF MONOUNARY ALGEBRAS

2012 ◽  
Vol 93 (3) ◽  
pp. 259-276 ◽  
Author(s):  
DANICA JAKUBÍKOVÁ-STUDENOVSKÁ ◽  
REINHARD PÖSCHEL ◽  
SÁNDOR RADELECZKI
Keyword(s):  
Partial Order ◽  
Unary Operation ◽  
Natural Order ◽  
Monounary Algebra ◽  
Natural Partial Order ◽  
Ordered Structure ◽  
Subdirectly Irreducible ◽  
Irreducible Elements ◽  
Algebraic Counterpart

AbstractRooted monounary algebras can be considered as an algebraic counterpart of directed rooted trees. We work towards a characterization of the lattice of compatible quasiorders by describing its join- and meet-irreducible elements. We introduce the limit $\cB _\infty $ of all $d$-dimensional Boolean cubes $\Two ^d$ as a monounary algebra; then the natural order on $\Two ^d$ is meet-irreducible. Our main result is that any completely meet-irreducible quasiorder of a rooted algebra is a homomorphic preimage of the natural partial order (or its inverse) of a suitable subalgebra of $\cB _\infty $. For a partial order, it is known that complete meet-irreducibility means that the corresponding partially ordered structure is subdirectly irreducible. For a rooted monounary algebra it is shown that this property implies that the unary operation has finitely many nontrivial kernel classes and its graph is a binary tree.

scholarly journals Endpoints inT0-Quasimetric Spaces: Part II

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Collins Amburo Agyingi ◽  
Paulus Haihambo ◽  
Hans-Peter A. Künzi
Keyword(s):  
Complete Lattice ◽  
Partially Ordered Set ◽  
Ordered Set ◽  
Partial Orders ◽  
Macneille Completion ◽  
Partially Ordered ◽  
Irreducible Elements ◽  
Quasimetric Space

We continue our work on endpoints and startpoints inT0-quasimetric spaces. In particular we specialize some of our earlier results to the case of two-valuedT0-quasimetrics, that is, essentially, to partial orders. For instance, we observe that in a complete lattice the startpoints (resp., endpoints) in our sense are exactly the completely join-irreducible (resp., completely meet-irreducible) elements. We also discuss for a partially ordered set the connection between its Dedekind-MacNeille completion and theq-hyperconvex hull of its naturalT0-quasimetric space.

scholarly journals Two Partial Orders for Standard Young Tableaux

10.37236/5967 ◽  
2019 ◽  
Vol 26 (3) ◽  
Author(s):  
Justyna Kosakowska ◽  
Markus Schmidmeier ◽  
Hugh Thomas
Keyword(s):  
Symmetric Group ◽  
Invariant Subspaces ◽  
Bruhat Order ◽  
Partial Orders ◽  
Linear Operators ◽  
Dominance Order ◽  
Representation Space ◽  
Young Tableaux ◽  
Standard Young Tableaux

In this manuscript we show that two partial orders defined on the set of standard Young tableaux of shape $\alpha$ are equivalent. In fact, we give two proofs for the equivalence of  the box order and the dominance order for tableaux. Both are algorithmic. The first of these proofs emphasizes links to the Bruhat order for the symmetric group and the second provides a more straightforward construction of the cover relations. This work is motivated by the known result that the equivalence of the two combinatorial orders leads to a description of the geometry of the representation space of invariant subspaces of nilpotent linear operators.

scholarly journals On induced permutation matrices and the symmetric group

1936 ◽  
Vol 5 (1) ◽  
pp. 1-13 ◽  
Author(s):  
A. C. Aitken
Keyword(s):  
Symmetric Group ◽  
Matrix Representation ◽  
Zero Element ◽  
Natural Order ◽  
Third Order ◽  
The Third ◽  
Permutation Matrices ◽  
The Matrix ◽  
Matrix Relation ◽  
Image Position

The n! operations Ai of permutations upon n different ordered symbols correspond to n! matrices Ai of the nth order, which have in each row and in each column only one non-zero element, namely a unit. Such matrices Ai are called permutation matrices, since their effect in premultiplying an arbitrary column vector x = {x1x2….xn} is to impress the permutation Ai upon the elements xi. For example the six matrices of the third orderare permutation matrices. It is convenient to denote them bywhere the bracketed indices refer to the permutations of natural order. Clearly the relation Ai Aj = Ak entails the matrix relation AiAj = Ak; in other words, the n! matrices Ai, give a matrix representation of the symmetric group of order n!.

scholarly journals The Bruhat order on conjugation-invariant sets of involutions in the symmetric group

2015 ◽  
Vol DMTCS Proceedings, 27th... (Proceedings) ◽  
Author(s):  
Mikael Hansson
Keyword(s):  
Fixed Point ◽  
Symmetric Group ◽  
Fixed Points ◽  
Bruhat Order ◽  
Rank Function ◽  
Invariant Sets ◽  
Graded Poset ◽  
International Audience ◽  
Complete Characterisation

12 pages, 3 figures International audience Let $I_n$ be the set of involutions in the symmetric group $S_n$, and for $A \subseteq \{0,1,\ldots,n\}$, let \[ F_n^A=\{\sigma \in I_n \mid \text{$\sigma$ has $a$ fixed points for some $a \in A$}\}. \] We give a complete characterisation of the sets $A$ for which $F_n^A$, with the order induced by the Bruhat order on $S_n$, is a graded poset. In particular, we prove that $F_n^{\{1\}}$ (i.e., the set of involutions with exactly one fixed point) is graded, which settles a conjecture of Hultman in the affirmative. When $F_n^A$ is graded, we give its rank function. We also give a short new proof of the EL-shellability of $F_n^{\{0\}}$ (i.e., the set of fixed point-free involutions), which was recently proved by Can, Cherniavsky, and Twelbeck. Soit $I_n$ l’ensemble d’involutions dans le groupe symétrique $S_n$, et pour $A \subseteq \{0,1,\ldots,n\}$, soit\[ F_n^A=\{\sigma \in I_n \mid \text{$\sigma$ a $a$ points fixes pour quelque $a \in A$}\}. \] Nous caractérisons tous les ensembles $A$ dont les $F_n^A$ , avec l’ordre induit par l’ordre de Bruhat sur $S_n$, est un posetgradué. En particulier, nous démontrons que $F_n^{\{1\}}$ (c’est-à-dire, l’ensemble d’involutions avec précis en point fixe)est gradué, ce qui résout une conjecture d’Hultman à l’affirmative. Lorsque $F_n^A$ est gradué, nous donnons sa fonctionde rang. En plus, nous donnons une nouvelle démonstration courte l’EL-shellability de $F_n^{\{0\}}$ (c’est-à-dire, l’ensembled’involutions sans points fixes), établie récemment par Can, Cherniavsky et Twelbeck.

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