290 research outputs found
A Generalization of the Ramanujan Polynomials and Plane Trees
Generalizing a sequence of Lambert, Cayley and Ramanujan, Chapoton has
recently introduced a polynomial sequence Q_n:=Q_n(x,y,z,t) defined by Q_1=1,
Q_{n+1}=[x+nz+(y+t)(n+y\partial_y)]Q_n. In this paper we prove Chapoton's
conjecture on the duality formula: Q_n(x,y,z,t)=Q_n(x+nz+nt,y,-t,-z), and
answer his question about the combinatorial interpretation of Q_n. Actually we
give combinatorial interpretations of these polynomials in terms of plane
trees, half-mobile trees, and forests of plane trees. Our approach also leads
to a general formula that unifies several known results for enumerating trees
and plane trees.Comment: 20 pages, 2 tables, 8 figures, see also
http://math.univ-lyon1.fr/~gu
Positivity properties of Jacobi-Stirling numbers and generalized Ramanujan polynomials
Generalizing recent results of Egge and Mongelli, we show that each diagonal
sequence of the Jacobi-Stirling numbers \js(n,k;z) and \JS(n,k;z) is a
P\'olya frequency sequence if and only if and study the
-total positivity properties of these numbers. Moreover, the polynomial
sequences \biggl\{\sum_{k=0}^n\JS(n,k;z)y^k\biggr\}_{n\geq 0}\quad \text{and}
\quad \biggl\{\sum_{k=0}^n\js(n,k;z)y^k\biggr\}_{n\geq 0} are proved to be
strongly -log-convex. In the same vein, we extend a recent result of
Chen et al. about the Ramanujan polynomials to Chapoton's generalized Ramanujan
polynomials. Finally, bridging the Ramanujan polynomials and a sequence arising
from the Lambert function, we obtain a neat proof of the unimodality of the
latter sequence, which was proved previously by Kalugin and Jeffrey.Comment: 17 pages, 2 tables, the proof of Lemma 3.3 is corrected, final
version to appear in Advances in Applied Mathematic
Multiple Gamma Function and Its Application to Computation of Series
The multiple gamma function , defined by a recurrence-functional
equation as a generalization of the Euler gamma function, was originally
introduced by Kinkelin, Glaisher, and Barnes around 1900. Today, due to the
pioneer work of Conrey, Katz and Sarnak, interest in the multiple gamma
function has been revived. This paper discusses some theoretical aspects of the
function and their applications to summation of series and infinite
products.Comment: 20 pages, Latex, uses kluwer.cls, will appear in The Ramanujan
Journa
Multiplicity estimates, analytic cycles and Newton polytopes
We consider the problem of estimating the multiplicity of a polynomial when
restricted to the smooth analytic trajectory of a (possibly singular)
polynomial vector field at a given point or points, under an assumption known
as the D-property. Nesterenko has developed an elimination theoretic approach
to this problem which has been widely used in transcendental number theory.
We propose an alternative approach to this problem based on more local
analytic considerations. In particular we obtain simpler proofs to many of the
best known estimates, and give more general formulations in terms of Newton
polytopes, analogous to the Bernstein-Kushnirenko theorem. We also improve the
estimate's dependence on the ambient dimension from doubly-exponential to an
essentially optimal single-exponential.Comment: Some editorial modifications to improve readability; No essential
mathematical change
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Coverings of Graphs and Tiered Trees
This dissertation will cover two separate topics. The first of these topics will be coverings of graphs. We will discuss a recent paper by Marcus, Spielman, and Srivastava proving the existence of infinite families of bipartite Ramanujan graphs for all regularities. The proof works by showing that for any d-regular Ramanujan graph, there exists an infinite tower of bipartite Ramanujan graphs in which each graph is a twofold covering of the previous one. Since twofold coverings of a graph correspond to ways of labeling the edges of the graph with elements of a group of order 2, we will generalize the content of the recent paper by discussing what happens when we label the edges of a graph by larger groups. We will give a version of their proof using threefold coverings instead of twofold coverings. We will also examine ways of reducing the size of the set of twofold coverings that we must consider when we follow the proof by Marcus, Spielman, and Srivastava.
The other topic that will be covered in this dissertation will be alternating trees and tiered trees. We will define a new generalization of alternating trees, which we will call tiered trees. We will also define a generalized weight system on these tiered trees. We will prove some enumerative results about tiered trees that demonstrate how they can be viewed as being obtained by applying certain procedures to certain types of alternating trees. We also provide a bijection between the set of permutations in Sn and the set of weight 0 alternating trees with n+1 vertices. We use this bijection to define a new statistic of permutations called the weight of a permutation, and use this weight to define a new q-Eulerian polynomial
A Survey of Alternating Permutations
This survey of alternating permutations and Euler numbers includes
refinements of Euler numbers, other occurrences of Euler numbers, longest
alternating subsequences, umbral enumeration of classes of alternating
permutations, and the cd-index of the symmetric group.Comment: 32 pages, 7 figure
Interlacing Ehrhart Polynomials of Reflexive Polytopes
It was observed by Bump et al. that Ehrhart polynomials in a special family
exhibit properties similar to the Riemann {\zeta} function. The construction
was generalized by Matsui et al. to a larger family of reflexive polytopes
coming from graphs. We prove several conjectures confirming when such
polynomials have zeros on a certain line in the complex plane. Our main new
method is to prove a stronger property called interlacing
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