17 research outputs found
Indecomposable Permutations, Hypermaps and Labeled Dyck Paths
Hypermaps were introduced as an algebraic tool for the representation of
embeddings of graphs on an orientable surface. Recently a bijection was given
between hypermaps and indecomposable permutations; this sheds new light on the
subject by connecting a hypermap to a simpler object. In this paper, a
bijection between indecomposable permutations and labelled Dyck paths is
proposed, from which a few enumerative results concerning hypermaps and maps
follow. We obtain for instance an inductive formula for the number of hypermaps
with n darts, p vertices and q hyper-edges; the latter is also the number of
indecomposable permutations of with p cycles and q left-to-right maxima. The
distribution of these parameters among all permutations is also considered.Comment: 30 pages 4 Figures. submitte
A Gray Code for the Shelling Types of the Boundary of a Hypercube
We consider two shellings of the boundary of the hypercube equivalent if one
can be transformed into the other by an isometry of the cube. We observe that a
class of indecomposable permutations, bijectively equivalent to standard double
occurrence words, may be used to encode one representative from each
equivalence class of the shellings of the boundary of the hypercube. These
permutations thus encode the shelling types of the boundary of the hypercube.
We construct an adjacent transposition Gray code for this class of
permutations. Our result is a signed variant of King's result showing that
there is a transposition Gray code for indecomposable permutations
Number of right ideals and a -analogue of indecomposable permutations
We prove that the number of right ideals of codimension in the algebra of
noncommutative Laurent polynomials in two variables over the finite field
is equal to , where the sum is over all indecomposable permutations in
and where stands for the number of inversions of
.Comment: submitte
On pattern avoiding indecomposable permutations
Comtet introduced the notion of indecomposable permutations in 1972. A permutation is indecomposable if and only if it has no proper prefix which is itself a permutation. Indecomposable permutations were studied in the literature in various contexts. In particular, this notion has been proven to be useful in obtaining non-trivial enumeration and equidistribution results on permutations. In this paper, we give a complete classification of indecomposable permutations avoiding a classical pattern of length 3 or 4, and of indecomposable permutations avoiding a non-consecutive vincular pattern of length 3. Further, we provide a recursive formula for enumerating 12 ••• k-avoiding indecomposable permutations for k ≥ 3. Several of our results involve the descent statistic. We also provide a bijective proof of a fact relevant to our studies
The Sorting Index and Permutation Codes
In the combinatorial study of the coefficients of a bivariate polynomial that
generalizes both the length and the reflection length generating functions for
finite Coxeter groups, Petersen introduced a new Mahonian statistic ,
called the sorting index. Petersen proved that the pairs of statistics
and have the same joint distribution over
the symmetric group, and asked for a combinatorial proof of this fact. In
answer to the question of Petersen, we observe a connection between the sorting
index and the B-code of a permutation defined by Foata and Han, and we show
that the bijection of Foata and Han serves the purpose of mapping
to . We also give a type analogue of the
Foata-Han bijection, and we derive the quidistribution of and over signed
permutations. So we get a combinatorial interpretation of Petersen's
equidistribution of and . Moreover, we show that
the six pairs of set-valued statistics ,
, , ,
and are equidistributed over signed
permutations. For Coxeter groups of type , Petersen showed that the two
statistics and are equidistributed. We introduce two statistics
and for elements of and we prove that the two
pairs of statistics and are
equidistributed.Comment: 25 page