20,465 research outputs found
The equivalence of two graph polynomials and a symmetric function
The U-polynomial, the polychromate and the symmetric function generalization of the Tutte polynomial due to Stanley are known to be equivalent in the sense that the coefficients of any one of them can be obtained as a function of the coefficients of any other. The definition of each of these functions suggests a natural way in which to strengthen them which also captures Tutte's universal V-function as a specialization. We show that the equivalence remains true for the strong functions thus
answering a question raised by Dominic Welsh
The Equivalence of Two Graph Polynomials and a Symmetric Function
The U-polynomial, the polychromate and the symmetric function generalization
of the Tutte polynomial due to Stanley are known to be equivalent in the sense
that the coefficients of any one of them can be obtained as a function of the
coefficients of any other. The definition of each of these functions suggests a
natural way in which to generalize them which also captures Tutte's universal
V-functions as a specialization. We show that the equivalence remains true for
the extended functions thus answering a question raised by Dominic Welsh.Comment: 17 page
A combinatorial proof that Schubert vs. Schur coefficients are nonnegative
We give a combinatorial proof that the product of a Schubert polynomial by a
Schur polynomial is a nonnegative sum of Schubert polynomials. Our proof uses
Assaf's theory of dual equivalence to show that a quasisymmetric function of
Bergeron and Sottile is Schur-positive. By a geometric comparison theorem of
Buch and Mihalcea, this implies the nonnegativity of Gromov-Witten invariants
of the Grassmannian.Comment: 26 pages, several colored figure
From the Ising and Potts models to the general graph homomorphism polynomial
In this note we study some of the properties of the generating polynomial for
homomorphisms from a graph to at complete weighted graph on vertices. We
discuss how this polynomial relates to a long list of other well known graph
polynomials and the partition functions for different spin models, many of
which are specialisations of the homomorphism polynomial.
We also identify the smallest graphs which are not determined by their
homomorphism polynomials for and and compare this with the
corresponding minimal examples for the -polynomial, which generalizes the
well known Tutte-polynomal.Comment: V2. Extended versio
The Potts model and chromatic functions of graphs
The -polynomial of Noble and Welsh is known to have intimate connections
with the Potts model as well as with several important graph polynomials. For
each graph , is equivalent to Stanley's symmetric bad colouring
polynomial . Moreover Sarmiento established the equivalence between
and the polychromate of Brylawski. Loebl defined the -dichromate
as a function of a graph and three independent variables
, proved that it is equal to the partition function of the Potts model
with variable number of states and with a certain external field contribution,
and conjectured that the -dichromate is equivalent to the -polynomial. He
also proposed a stronger conjecture on integer partitions. The aim of this
paper is two-fold. We present a construction disproving Loebl's integer
partitions conjecture, and we introduce a new function which
is also equal to the partition function of the Potts model with variable number
of states and with a (different) external field contribution, and we show that
is equivalent to the -polynomial and to Stanley's symmetric
bad colouring polynomial
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