Codeterminants for the Symplectic Schur Algebra

Standard codeterminants for Donkin's symplectic Schur algebra are defined. It is shown that they form a basis of . They are then used to give a purely combinatorial proof that is quasi-hereditary.     

Ribbon Schur Functions

We present a new determinantal expression for Schur functions. Previous expressions were due to Jacobi, Trudi, Giambelli and others (see [7]) and involved elementary symmetric functions or hook functions. We give, in Theorem 1.1, a decomposition of a Schur function into ribbon functions (also called skew hook functions, new functions by MacMahon, and MacMahon functions by others). We provide two different proofs of this result in Sections 2 and 3. In Section 2, we use Bazin's formula for the minors of a general matrix, as we already did in [6], to decompose a skew Schur function into hooks. In Section 3, we show how to pass from hooks to ribbons and conversely. In Section 4, we generalize to skew Schur functions. In Section 5, we give some applications, and show how such constructions, in the case of staircase partitions, generalize the classical continued fraction for the tangent function due to Euler.     

Equality of Schur and Skew Schur Functions

We determine the precise conditions under which any skew Schur function is equal to a Schur function over both infinitely and finitely many variables. Received May 29, 2004     

Multiplicity Free Schur, Skew Schur, and Quasisymmetric Schur Functions

In this paper we classify all Schur functions and skew Schur functions that are multiplicity free when expanded in the basis of fundamental quasisymmetric functions, termed F-multiplicity free. Combinatorially, this is equivalent to classifying all skew shapes whose standard Young tableaux have distinct descent sets. We then generalize our setting, and classify all F-multiplicity free quasisymmetric Schur functions with one or two terms in the expansion, or one or two parts in the indexing composition. This identifies composition shapes such that all standard composition tableaux of that shape have distinct descent sets. We conclude by providing such a classification for quasisymmetric Schur function families, giving a classification of Schur functions that are in some sense almost F-multiplicity free.     

Row-Strict Quasisymmetric Schur Functions

Haglund, Luoto, Mason, and van Willigenburg introduced a basis for quasisymmetric functions, called the quasisymmetric Schur function basis, generated combinatorially through fillings of composition diagrams in much the same way as Schur functions are generated through reverse column-strict tableaux. We introduce a new basis for quasisymmetric functions, called the row-strict quasisymmetric Schur function basis, generated combinatorially through fillings of composition diagrams in much the same way as quasisymmetic Schur functions are generated through fillings of composition diagrams. We describe the relationship between this new basis and other known bases for quasisymmetric functions, as well as its relationship to Schur polynomials. We obtain a refinement of the omega transform operator as a result of these relationships.     

Lagrange Inversion and Schur Functions

Macdonald defined an involution on symmetric functions by considering the Lagrange inverse of the generating function of the complete homogeneous symmetric functions. The main result we prove in this note is that the images of skew Schur functions under this involution are either Schur positive or Schur negative symmetric functions. The proof relies on the combinatorics of Lagrange inversion. We also present a q-analogue of this result, which is related to the q-Lagrange inversion formula of Andrews, Garsia, and Gessel, as well as the operator of Bergeron and Garsia.     

Multiplicity-Free Products of Schur Functions

. We classify all multiplicity-free products of Schur functions and all multiplicity-free products of characters of SL(n, C).     

On Negative Inertia of Pick Matrices Associated with Generalized Schur Functions

It is known [6] that for every function f in the generalized Schur class and every nonempty open subset Ω of the unit disk , there exist points z₁,...,z_n ∈Ω such that the n × nPick matrix has κ negative eigenvalues. In this paper we discuss existence of an integer n₀ such that any Pick matrix based on z₁,...,z_n ∈Ω with n ≥ n₀ has κ negative eigenvalues. Definitely, the answer depends on Ω. We prove that if , then such a number n₀ does not exist unless f is a ratio of two finite Blaschke products; in the latter case the minimal value of n₀ can be found. We show also that if the closure of Ω is contained in then such a number n₀ exists for every function f in .     

On Rank Invariance of Schwarz-Pick-Potapov Block Matrices of Matricial Schur Functions

We derive statements on rank invariance of Schwarz-Pick-Potapov block matrices of matrix-valued Schur functions. The rank of these block matrices coincides with the rank of some block matrices built from the corresponding section matrices of Taylor coefficients. These results are applied to the discussion of a matrix version of the classical Schur-Nevanlinna algorithm.     

The Schur Algorithm for Generalized Schur Functions II: Jordan Chains and Transformations of Characteristic Functions

 In the first paper of this series (Daniel Alpay, Tomas Azizov, Aad Dijksma, and Heinz Langer: The Schur algorithm for generalized Schur functions I: coisometric realizations, Operator Theory: Advances and Applications 129 (2001), pp. 1–36) it was shown that for a generalized Schur function s(z), which is the characteristic function of a coisometric colligation V with state space being a Pontryagin space, the Schur transformation corresponds to a finite-dimensional reduction of the state space, and a finite-dimensional perturbation and compression of its main operator. In the present paper we show that these formulas can be explained using simple relations between V and the colligation of the reciprocal s(z)⁻¹ of the characteristic function s(z) and general factorization results for characteristic functions. Received October 31, 2001; in revised form August 21, 2002 RID="a" ID="a" Dedicated to Professor Edmund Hlawka on the occasion of his 85th birthday     

Interpolation, Schur Functions and Moment Problems

No Abstract.  .     

Unimodality of Differences of Specialized Schur Functions

The centered difference of principally specialized Schur functions

On Schur Superfunctors

We introduce super-analogues of the Schur functors defined by Akin, Buchsbaum and Weyman. These Schur superfunctors may be viewed as characteristic-free analogues of finite dimensional irreducible polynomial representations of the Lie superalgebra ????(m|n) studied by Berele and Regev. Our construction realizes Schur superfunctors as objects of a certain category of strict polynomial superfunctors. We show that Schur superfunctors are indecomposable objects of this category. In characteristic zero, these correspond to the set of all simple supermodules for the Schur superalgebra, S(m|n, d), for any m, n, d ? 0. We also provide decompositions of Schur bisuperfunctors in terms of tensor products of skew Schur superfunctors.     

奇变元Semibent-negabent函数的构造

研究negabent函数之间的关系,并利用bent-negabent函数构造出代数次数达到次最优的semibent-negabent函数.     

完全对称函数的Schur凸性

定义了一完全对称函数并研究该称函数的Schur凸性,Schur乘性凸性及Schur调和凸性,作为应用探讨了与其相关的一些不等式.     

Kernel Decompositions for Schur Functions on the Polydisk

A certain kernel (sometimes called the Pick kernel) associated to Schur functions on the disk is always positive semi-definite. A generalization of this fact is well-known for Schur functions on the polydisk. In this article, we show that the “Pick kernel” on the polydisk has a great deal of structure beyond being positive semi-definite. It can always be split into two kernels possessing certain shift invariance properties.     

Using Hook Schur Functions to Compute Matrix Cocharacters

We develop a new integration method based on hook Schur functions instead of Schur functions to compute the cocharacters of matrices. We then use this method to compute some of the multiplicities in the cocharacter sequence of 3 × 3 matrices.