Groupoid Approach to Ergodic Dynamical System of Commutative von Neumann Algebra

Given a compact and regular Hausdorff measure space (X, μ), with μ a Radon measure, it is known that the generalised space M(X) of all the positive Radon measures on X is isomorphic to the space of essentially bounded functions L∞(X, μ) on X. We confirm that the commutative von Neumann algebras M⊂B(H), with H=L2(X, μ), are unitary equivariant to the maximal ideals of the commutative algebra C(X). Subsequenly, we use the measure groupoid to formulate the algebraic and topological structures of the commutative algebra C(X) following its action on M(X) and define its representation and ergodic dynamical system on the commutative von Neumann algebras of M of B(H) .

Poisson groupoid的余迷向双截面

Poisson groupoid是Weinstein在研究PoissonLie群和辛groupoid时提出的一个新概念 .本文对Poisson groupoid中较重要的余迷向双截面做了一定的讨论 。

左不变作用生成的Groupoid C—代数动力系统

本文引进了由左不变作用生成的ＧｒｏｕｐｏｉｄＣ＊－代数动力系统．研究了它与由１－ｃｏｃｙｃｌｅ生成的ＧｒｏｕｖｏｉｄＣ＊－代数动力系统的关系．得到了两个共变同构定理及两个对偶定理．

Duality theorem for smash coproduct over quantum groupoids

The duality theorem of generalized weak smash coproducts of weak module coalgebras and comodule coalgebras over quantum groupoids is studied.Let H be a weak Hopf algebra,C a left weak H-comodule coalgebra and D a left weak H-module coalgebra.First,a weak generalized smash coproduct C×lH D over quantum groupoids is defined and the module and comodule structures on it are constructed.The weak generalized right smash coproduct C×rL D is similar.Then some isomorph-isms between them are obtained.Secondly,by introducing some concepts of a weak convolution invertible element,a weak co-inner coaction and a strongly relative co-inner coaction,a sufficient condition for C×rH D to be isomorphic to Cv D is obtained,where v∈WC（C,H）and the coaction of H on D is right strongly relative co-inner.Finally,the duality theorem for a generalized smash coproduct over quantum groupoids,（C×lH H）×lH H≌Cv（H×lH H）,is obtained.

Groupoids,Discrete Mechanics,and Discrete Variation

After introducing some of the basic definitions and results from the theory of groupoid and Lie algebroid,we investigate the discrete Lagrangian mechanics from the viewpoint of groupoid theory and give the connection betweengroupoids variation and the methods of the first and second discrete variational principles.

Causal Groupoid Symmetries and Big Data

The big problem of Big Data is the lack of a machine learning process that scales and finds meaningful features. Humans fill in for the insufficient automation, but the complexity of the tasks outpaces the human mind’s capacity to comprehend the data. Heuristic partition methods may help but still need humans to adjust the parameters. The same problems exist in many other disciplines and technologies that depend on Big Data or Machine Learning. Proposed here is a fractal groupoid-theoretical method that recursively partitions the problem and requires no heuristics or human intervention. It takes two steps. First, make explicit the fundamental causal nature of information in the physical world by encoding it as a causal set. Second, construct a functor F: C C′ on the category of causal sets that morphs causal set C into smaller causal set C′ by partitioning C into a set of invariant groupoid-theoretical blocks. Repeating the construction, there arises a sequence of progressively smaller causal sets C, C′, C″, … The sequence defines a fractal hierarchy of features, with the features being invariant and hence endowed with a physical meaning, and the hierarchy being scale-free and hence ensuring proper scaling at all granularities. Fractals exist in nature nearly everywhere and at all physical scales, and invariants have long been known to be meaningful to us. The theory is also of interest for NP-hard combinatorial problems that can be expressed as a causal set, such as the Traveling Salesman problem. The recursive groupoid partition promoted by functor F works against their combinatorial complexity and appears to allow a low-order polynomial solution. A true test of this property requires special hardware, not yet available. However, as a proof of concept, a suite of sequential, non-heuristic algorithms were developed and used to solve a real-world 120-city problem of TSP on a personal computer. The results are reported.

Causal Groupoid Symmetries

Proposed here is a new framework for the analysis of complex systems as a non-explicitly programmed mathematical hierarchy of subsystems using only the fundamental principle of causality, the mathematics of groupoid symmetries, and a basic causal metric needed to support measurement in Physics. The complex system is described as a discrete set S of state variables. Causality is described by an acyclic partial order w on S, and is considered as a constraint on the set of allowed state transitions. Causal set (S, w) is the mathematical model of the system. The dynamics it describes is uncertain. Consequently, we focus on invariants, particularly group-theoretical block systems. The symmetry of S by itself is characterized by its symmetric group, which generates a trivial block system over S. The constraint of causality breaks this symmetry and degrades it to that of a groupoid, which may yield a non-trivial block system on S. In addition, partial order w determines a partial order for the blocks, and the set of blocks becomes a causal set with its own, smaller block system. Recursion yields a multilevel hierarchy of invariant blocks over S with the properties of a scale-free mathematical fractal. This is the invariant being sought. The finding hints at a deep connection between the principle of causality and a class of poorly understood phenomena characterized by the formation of hierarchies of patterns, such as emergence, selforganization, adaptation, intelligence, and semantics. The theory and a thought experiment are discussed and previous evidence is referenced. Several predictions in the human brain are confirmed with wide experimental bases. Applications are anticipated in many disciplines, including Biology, Neuroscience, Computation, Artificial Intelligence, and areas of Engineering such as system autonomy, robotics, systems integration, and image and voice recognition.

Groupoid C~■_代数中的自反子代数

讨论了ＧｒｏｕｐｏｉｄＣ＿代数中子代数的三种自反性的概念及三者之间的关系．

Differential Groupoids

The basic properties and some examples of the differential groupoids are studied.

Groupoid的诱导表示

设Ｇ为第二可数局部紧有Ｈａａｒ系的Ｇｒｏｕｐｏｉｄ， Ｈ为子Ｇｒｏｕｐｏｉｄ闭于Ｇ，则可得Ｇｒｏｕｐｏｉｄ Ｈ＼Ｇ２，我们证明了Ｃ＊（Ｈ）与Ｃ＊（Ｈ＼Ｇ２）是Ｍｏｒｉｔａ等价的，从而回答了［１］中的问题．利用此非本原双模及定义Ｃ＊（Ｇ）到Ｍ（Ｃ＊（Ｈ＼Ｇ２））的映射，得到了由Ｃ＊（Ｈ）到Ｃ＊（Ｇ）的诱导表示．特别在群丛情形，我们定义了Ｃ＊（Ｈ）→Ｍ（Ｃ＊（Ｇ））的映射，并具体得到了诱导表示的积分形式的表达式．

n-transitivity of Bisection Groups of a Lie Groupoid

The notion of n-transitivity can be carried over from groups of diffeomorphisms on a manifold M to groups of bisections of a Lie groupoid over M. The main theorem states that the n-transitivity is fulfilled for all n ∈N by an arbitrary group of Cr-bisections of a Lie groupoid F of class Cr, where 1 ≤ r ≤ ω, under mild conditions. For instance, the group of all bisections of any Lie groupoid and the group of all Lagrangian bisections of any symplectic groupoid are n-transitive in the sense of this theorem. In particular, if F is source connected for any arrow γ∈ Г, there is a bisection passing through γ.

On the Existence of Global Bisections of Lie Groupoids

We show that every source connected Lie groupoid always has global bisections through any given point. This bisection can be chosen to be the multiplication of some exponentials as close as possible to a prescribed curve. The existence of bisections through more than one prescribed point is also discussed. We give some interesting applications of these results.

Spectral Invariant Subalgebras of Reduced Groupoid C^＊-algebras

We introduce the notion of property(RD) for a locally compact, Hausdorff and r-discrete groupoid G, and show that the set S~l(G) of rapidly decreasing functions on G with respect to a continuous length function l is a dense spectral invariant and Fréchet *-subalgebra of the reduced groupoid C~*-algebra C~*(G) of G when G has property(RD) with respect to l, so the K-theories of both algebras are isomorphic under inclusion. Each normalized cocycle c on G, together with an invariant probability measure on the unit space G~0 of G, gives rise to a canonical map τon the algebra C(G) of complex continuous functions with compact support on G. We show that the map τcan be extended continuously to S~l(G) and plays the same role as an n-trace on C~*(G) when G has property(RD) and c is of polynomial growth with respect to l, so the Connes’ fundament paring between the K-theory and the cyclic cohomology gives us the K-theory invariants on C~*(G).

自同构系统的拓扑刚性

研究了可数离散群在紧度量空间étale等价关系上的自同构作用。文章引入了自同构系统上连续强轨道等价的定义,证明了共轭的两个自同构系统一定是连续强轨道等价的,反之,在本质自由和离散群是顺从无挠的条件下,满足刚性条件的两个连续强轨道等价的自同构系统是共轭的。

Submodules of the groupoid C~*-algebra

Given an r-discrete, principal and amenable groupoid, the bijective correspondence between the family c the closedC o(G 0)-bimodules ofC(G) and the family of the open subsets of the groupoidG is established. More over they are rigidity.

Square Integrable Representation of Groupoids

A notion of an irreducible representation, as well as of a square integrable representation on an arbitrary locally compact groupoid, is introduced. A generalization of a version of Schur＇s lemma on a locally compact groupoid is given. This is used in order to extend some well-known results from locally compact groups to the case of locally compact groupoids. Indeed, we have proved that if L is a continuous irreducible representation of a compact groupoid G defined by a continuous Hilbert bundle H = （Hu）u∈G^0, then each Hu is finite dimensional. It is also shown that if L is an irreducible representation of a principal locally compact groupoid defined by a Hilbert bundle （G^0, （Hu）,μ）, then dimHu = 1 （u ∈ G^0）. Furthermore it is proved that every square integrable representation of a locally compact groupoid is unitary equivalent to a subrepresentation of the left regular representation. Furthermore, for r-discrete groupoids, it is shown that every irreducible subrepresentation of the left regular representation is square integrable.

Crossed Products on the Flow of Groupoid with Quasi-Invariant Measures

Let G be a second countable groupoid with Haar system {λ~u}, A be an abelian group which left invariant acts on G. Then we have a C*-dynamic system (C*(G), A, β). In this paper we have studied the existence of quasi-invariant measure with certain properties; using these measures some important results about crossed products and groupoid C*-algebras have been obtained.

On Semilattice Decomposition of an Abel–Grassmann’s Groupoid

In this paper, we have decomposed an AG-groupoid. Let S be an AG-groupoid with left identity and a relation γ be defined on S as： aγb if and only if there exist positive integers m and n such that b^m∈E （Sa）S and a^n ∈ （Sb）S for all a and b in S. We have proved that S/γ is a maximal separative Semilattice homomorphic image of S. Every AG-groupoid S is uniquely expressible as a semilattice Y of archimedean AG-groupoids Sa （a∈ Y）. The semilattice Y is isomorphic to S/γ and the Sγ （a ∈ Y） are the equivalence classes of S mod V.

An Analogy of Clifford Decomposition Theorem for Abel-Grassmann Groupoids

Let S be an inverse AG-groupoid （Abel-Grassmann groupoid） and define a relation γ on S by aγb if and only if there exist some positive integers n and m such that bm∈ （Sa）S and an∈ （Sb）S. We prove that S/γ is a maximal semilattice homomorphic image of S. Thus, every inverse AG-groupoid S is uniquely expressible as a semilattice Y of some Archimedean inverse AG-groupoids Sα （α∈ Y）. Our result can be regarded as an analogy of the well known Clifford theorem in semigroups for AG-groupoids.

Nonlinear Conformal Gravitation

In 1909 the brothers E. and F. Cosserat discovered a new nonlinear group theoretical approach to elasticity (EL), with the only experimental need to measure the EL constants. In a modern framework, they used the nonlinear Spencer sequence instead of the nonlinear Janet sequence for the Lie groupoid defining the group of rigid motions of space. Following H. Weyl, our purpose is to compute for the first time the linear and nonlinear Spencer sequences for the Lie groupoid defining the conformal group of space-time in order to provide the mathematical foundations of both electromagnetism (EM) and gravitation (GR), with the only experimental need to measure the EM and GR constants. With a manifold of dimension n ≥ 3, the difficulty is to deal with the n nonlinear transformations that have been called “elations” by E. Cartan in 1922. Using the fact that dimension n = 4 has very specific properties for the computation of the Spencer cohomology, we also prove that there is no conceptual difference between the (nonlinear) Cosserat EL field or induction equations and the (linear) Maxwell EM field or induction equations. As for gravitation, the dimension n = 4 also allows to have a conformal factor defined everywhere but at the central attractive mass because the inversion law of the isotropy subgroupoid made by second order jets transforms attraction into repulsion. The mathematical foundations of both electromagnetism and gravitation are thus only depending on the structure of the conformal pseudogroup of space-time.