Noncommutative Symmetric Functions VII: Free Quasi-Symmetric Functions Revisited

We prove a Cauchy identity for free quasi-symmetric functions and apply it to the study of various bases. A free Weyl formula and a generalization of the splitting formula are also discussed.     

Acyclic Complexes Related to Noncommutative Symmetric Functions

In this paper, we show how to endow the algebra of noncommutative symmetric functions with a natural structure of cochain complex which strongly relies on the combinatorics of ribbons, and we prove that the corresponding complexes are acyclic.     

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.     

Colored Posets and Colored Quasisymmetric Functions

The colored quasisymmetric functions, like the classic quasisymmetric functions, are known to form a Hopf algebra with a natural peak subalgebra. We show how these algebras arise as the image of the algebra of colored posets. To effect this approach, we introduce colored analogs of P-partitions and enriched P-partitions. We also frame our results in terms of Aguiar, Bergeron, and Sottile’s theory of combinatorial Hopf algebras and its colored analog.     

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.     

Isometries on Noncommutative Symmetric Spaces

Doklady Mathematics - Let $$\mathcal{M}$$ be an atomless semifinite von Neumann algebra equipped with a faithful normal semifinite trace τ (or else, an atomic von Neumann algebra with all...     

Noncommutative Symmetric Functions Iv: Quantum Linear Groups and Hecke Algebras at q = 0

We present representation theoretical interpretations ofquasi-symmetric functions and noncommutative symmetric functions in terms ofquantum linear groups and Hecke algebras at q = 0. We obtain inthis way a noncommutative realization of quasi-symmetric functions analogousto the plactic symmetric functions of Lascoux and Schützenberger. Thegeneric case leads to a notion of quantum Schur function.     

Elementary Symmetric Functions

This section appears in nearly every issue. Send submissions to R. C. Thompson, at the Department of Mathematics, University of California, Stanta Barbara, CA 93106, U.S.A.     

Soliton Theory, Symmetric Functions and Matrix Integrals

We consider a certain scalar product of symmetric functions which is parameterized by a function r and an integer n. On the one hand we have a fermionic representation of this scalar product. On the other hand we get a representation of this product with the help of multi-integrals. This gives links between a theory of symmetric functions, soliton theory and models of random matrices (such as a model of normal matrices).     

Inner Functions, Bloch Spaces and Symmetric Measures

Schwarz's lemma asserts that analytic mappings from the unitdisc into itself decrease hyperbolic distances. In this paper,inner functions which decrease hyperbolic distances as muchas possible, when one approaches the unit circle, are constructed.Actually, it is shown that a quadratic condition governs thebest decay of the hyperbolic derivative of an inner function.This is related to a result of L. Carleson on the existenceof singular symmetric measures. As a consequence, some resultson composition operators are obtained, bringing out the importanceof the Bloch spaces in this connection. Another consequenceis a uniform way of producing singular measures which are simultaneouslysymmetric and Kahane. 1991 Mathematics Subject Classification:primary 30D50; secondary 30D45, 26A30, 47B38.     

Cyclic Tableaux and Symmetric Functions

We introduce the notion of cyclic tableaux and develop involutions for Waring's formulas expressing the power sum symmetric function p_n in terms of the elementary symmetric function e_n and the homogeneous symmetric function h_n. The coefficients appearing in Waring's formulas are shown to be a cyclic analog of the multinomial coefficients, a fact that seems to have been neglected before. Our involutions also spell out the duality between these two forms of Waring's formulas, which turns out to be exactly the “duality between sets and multisets.” We also present an involution for permutations in cycle notation, leading to probably the simplest combinatorial interpretation of the Möbius function of the partition lattice and a purely combinatorial treatment of the fundamental theorem on symmetric functions. This paper is motivated by Chebyshev polynomials in connection with Waring's formula in two variables.     

Schwinger Functions in Noncommutative Quantum Field Theory

It is shown that the n-point functions of scalar massive free fields on the noncommutative Minkowski space are distributions which are boundary values of analytic functions. Contrary to what one might expect, this construction does not provide a connection to the popular traditional Euclidean approach to noncommutative field theory (unless the time variable is assumed to commute). Instead, one finds Schwinger functions with twistings involving only momenta that are on the mass-shell. This explains why renormalization in the traditional Euclidean noncommutative framework crudely differs from renormalization in the Minkowskian regime.     

Tyson型集及Borel函数的图的拟对称极小性

本文将欧氏空间R^d中形如[0,1]×Z的集称为Tyson型集,其中d>1,Z⊂R^d-1.已知当Z是R^d-1中的紧集时,Tyson型集是拟对称极小集.本文改进了这个结果,证明了当Z是R^d-1中的Borel集时,Tyson型集仍是拟对称极小集.作为应用,我们证明了Tyson型集三个形变版本的拟对称极小性,其中一个结果是：设Z是R^d-1中的任一Borel集,h：Z→R¹是Borel函数,满足dim_H（{h≠0}∩Z）=dim_H Z,则h的图G（h）是拟对称极小集,其中h的图G（h）定义为G（h）={（z,y）：z∈Z,y∈[0,h（z）]}.     

Quasisymmetric groups

One of the first problems in the theory of quasisymmetric and convergence groups was to investigate whether every quasisymmetric group that acts on the sphere , , is a quasisymmetric conjugate of a Möbius group that acts on . This was shown to be true for by Sullivan and Tukia, and it was shown to be wrong for by Tukia. It also follows from the work of Martin and of Freedman and Skora. In this paper we settle the case of by showing that any -quasisymmetric group is -quasisymmetrically conjugated to a Möbius group. The constant is a function .

     

Little Bloch Functions, Symmetric Pluriharmonic Measures, and Zygmund's Dichotomy

We introduce special Riesz products on the complex sphere and prove Zygmund's dichotomy for such products. Given d ₊, this construction yields a d-pluriharmonic measure μ such that all slices of μ are singular and uniformly symmetric. In particular, there exist non-constant little Bloch inner functions in the complex ball. Further little Bloch applications are given.     

The Jacobi Matrix for Functions in Noncommutative Algebras

We develop a general tool for constructing the exact Jacobi matrix for functions defined in noncommutative algebraic systems without using any partial derivative. The construction is applied to solving nonlinear problems of the form f(x) = 0 with the aid of Newton’s method in algebras defined in \({\mathbb{R}^N}\) . We apply this to eight (commutative and noncommutative) algebras in \({\mathbb{R}^4}\) . The Jacobi matrix is explicitly constructed for polynomials in x?a and for polynomials in the reciprocals (x?a)¹ such that Jacobi matrices for functions defined by Taylor and Laurent expansions can be constructed in general algebras over \({\mathbb{R}^N}\) . The Jacobi matrix for the algebraic Riccati equation with matrix elements from an algebra in \({\mathbb{R}^N}\) is presented, and one particular algebraic Riccati equation is numerically solved in all eight algebras over \({\mathbb{R}^4}\) . Another case treated was the exponential function with algebraic variables including a numerical example. For cases where the computation of the exact Jacobi matrix for finding solutions of f(x) = 0 is time consuming, a hybrid method is recommended, namely to start with an approximation of the Jacobi matrix in low precision and only when \({\|f(x)\|}\) is sufficiently small, to switch to the exact Jacobi matrix.