On location models for ubiquitous computing

Common queries regarding information processing in ubiquitous computing are based on the location of physical objects. No matter whether it is the next printer, next restaurant, or a friend is searched for, a notion of distances between objects is required. A search for all objects in a certain geographic area requires the possibility to define spatial ranges and spatial inclusion of locations. In this paper, we discuss general properties of symbolic and geometric coordinates. Based on that, we present an overview of existing location models allowing for position, range, and nearest neighbor queries. The location models are classified according to their suitability with respect to the query processing and the involved modeling effort along with other requirements. Besides an overview of existing location models and approaches, the classification of location models with respect to application requirements can assist developers in their design decisions.     

On computing minimal independent support and its applications to sampling and counting

Constrained sampling and counting are two fundamental problems arising in domains ranging from artificial intelligence and security, to hardware and software testing. Recent approaches to approximate solutions for these problems rely on employing SAT solvers and universal hash functions that are typically encoded as XOR constraints of length n/2 for an input formula with n variables. As the runtime performance of SAT solvers heavily depends on the length of XOR constraints, recent research effort has been focused on reduction of length of XOR constraints. Consequently, a notion of Independent Support was proposed, and it was shown that constructing XORs over independent support (if known) can lead to a significant reduction in the length of XOR constraints without losing the theoretical guarantees of sampling and counting algorithms. In this paper, we present the first algorithmic procedure (and a corresponding tool, called MIS) to determine minimal independent support for a given CNF formula by employing a reduction to group minimal unsatisfiable subsets (GMUS). By utilizing minimal independent supports computed by MIS, we provide new tighter bounds on the length of XOR constraints for constrained counting and sampling. Furthermore, the universal hash functions constructed from independent supports computed by MIS provide two to three orders of magnitude performance improvement in state-of-the-art constrained sampling and counting tools, while still retaining theoretical guarantees.     

Efficiently computing minimal sets of critical pairs

In the computation of a Gröbner basis using Buchberger’s algorithm, a key issue for improving the efficiency is to produce techniques for avoiding as many unnecessary critical pairs as possible. A good solution would be to avoid all non-minimal critical pairs, and hence to process only a minimal set of generators of the module generated by the critical syzygies. In this paper we show how to obtain that desired solution in the homogeneous case while retaining the same efficiency as with the classical implementation. As a consequence, we get a new optimized Buchberger algorithm.     

面向云计算环境的访问控制模型

针对云计算[1]领域中基础设施服务在运行和管理中存在的安全问题,在传统访问控制模型的基础上综合考虑了云计算基础设施服务[2]的特点,设计了一套访问控制模型。分析了云计算中安全问题的特点及现有方案的不足之处,提出基础设施服务的安全是云计算安全的基础。根据四条设计原则在RBAC模型[3]和TE模型[4]的基础上加以改进形成了适用于云计算基础设施服务的CIRBAC模型和CITE模型,对模型中的各个模块进行了详细的设计。在基于Xen[5-6]虚拟化技术[7]的OpenStack[8]云计算环境中实现了这些访问控制模型。该模型很好地增强了云计算基础设施服务的安全性。     

Machines and models for parallel computing

It is widely believed that superscalar and superpipelined extensions of RISC style architecture will dominate future processor design, and that needs of parallel computing will have little effect on processor architecture. This belief ignores the issues of memory latency and synchronization, and fails to recognize the opportunity to support a general semantic model for parallel computing. Efforts to extend the shared-memory model using standard microprocessors have led to systems that implement no satisfactory model of computing, and present the programmer with a difficult interface on which to build parallel computing applications. A more satisfactory model for parallel computing may be obtained on the basis of functional programming concepts and the principles of modular software construction. We recommend that designs for computers be built on such a general semantic model of parallel computation. Multithreading concepts and dataflow principles can frame the architecture of these new machines.     

On computing pi-coefficients

Introduced by Lawrence and Johnson in 1986, the concept of pi-sharing can be used to analyze the stability of discrete-time systems. However, to determine the suitable pi-coefficients required in the application of pi-sharing theory is in general a difficult task. It involves checking the negative semi-definiteness (n.s.d.) of a complicated matrix. This paper formulates an alternative problem, the max-p problem, for determining the ‘best’ pi-coefficients, and proposes a solution method for the problem. The n.s.d. condition is turned into conditions on the coefficients of a series of polynomials, which are easier to solve than the original one. An example is used to illustrate the procedure in detail.     

On minimal graphs

Graphs, regarded as grammar forms as well as coloring specifications, induce graph-families, so-called color-families. It can be shown that for each color-family a unique (vertex) minimal graph exists. In this paper an operation on such minimal graphs is presented. As a main result it is shown that in a minimal graph G with m vertices, none of them adjacent to all other vertices, cliques have less than $\text{1}\text{2}$m vertices and this bound cannot be improved.     

Multirate sampled-data systems: computing fast-rate models

This paper studies identification of a general multirate sampled-data system. Using the lifting technique, we associate the multirate system with an equivalent linear time-invariant system, from which a fast-rate discrete-time system is extracted. Uniqueness of the fast-rate system, controllability and observability of the lifted system, and other related issues are discussed. The effectiveness is demonstrated through simulation and real-time implementation.     

DNA计算模型发展分析

概述了DNA计算的起源和发展,对几种常用的DNA计算模型,如剪接模型、粘贴模型、等同检测模型等进行了介绍和分析,展望了今后DNA计算模型发展的趋势。     

Computational and mathematical models meet heterogeneous computing

The Journal of Supercomputing -     

On the use of models for high-performance scientific computing applications: an experience report

This paper reports on a four-year project that aims to raise the abstraction level through the use of model-driven engineering (MDE) techniques in the development of scientific applications relying on high-performance computing. The development and maintenance of high-performance scientific computing software is reputedly a complex task. This complexity results from the frequent evolutions of supercomputers and the tight coupling between software and hardware aspects. Moreover, current parallel programming approaches result in a mixing of concerns within the source code. Our approach relies on the use of MDE and consists in defining domain-specific modeling languages targeting various domain experts involved in the development of HPC applications, allowing each of them to handle their dedicated model in a both user-friendly and hardware-independent way. The different concerns are separated thanks to the use of several models as well as several modeling viewpoints on these models. Depending on the targeted execution platforms, these abstract models are translated into executable implementations by means of model transformations. To make all of these effective, we have developed a tool chain that is also presented in this paper. The approach is assessed through a multi-dimensional validation that focuses on its applicability, its expressiveness and its efficiency. To capitalize on the gained experience, we analyze some lessons learned during this project.     

On computing logic programs

In this paper we present and compare some classical problem-solving methods for computing the stable models of logic programs with negation. Using a graph theoretic representation of logic programs and their stable models, we discuss and compare linear programming, propositional satisfiability, constraint satisfaction, and graph methods.     

On computing output-error estimates

In this note, we consider a system with rational transfer function from input to output where this transfer function haspparameters. It is also supposed that the input has a spectrum consisting ofpdistinct points (equivalently, we suppose that the design index =p/2). As proved in [2], this implies that the output-error estimator has the same efficiency as the prediction-error estimator. We present a very convenient algorithm for computing the output-error estimate of the transfer function from input to output.     

High performance computing for three-dimensional agent-based molecular models

Agent-based simulations are increasingly popular in exploring and understanding cellular systems, but the natural complexity of these systems and the desire to grasp different modelling levels demand cost-effective simulation strategies and tools.In this context, the present paper introduces novel sequential and distributed approaches for the three-dimensional agent-based simulation of individual molecules in cellular events. These approaches are able to describe the dimensions and position of the molecules with high accuracy and thus, study the critical effect of spatial distribution on cellular events. Moreover, two of the approaches allow multi-thread high performance simulations, distributing the three-dimensional model in a platform independent and computationally efficient way.Evaluation addressed the reproduction of molecular scenarios and different scalability aspects of agent creation and agent interaction. The three approaches simulate common biophysical and biochemical laws faithfully. The distributed approaches show improved performance when dealing with large agent populations while the sequential approach is better suited for small to medium size agent populations.Overall, the main new contribution of the approaches is the ability to simulate three-dimensional agent-based models at the molecular level with reduced implementation effort and moderate-level computational capacity. Since these approaches have a generic design, they have the major potential of being used in any event-driven agent-based tool.     

Distributed coordination models for client/server computing

A major limitation in the basic client/server model is its focus on clients requesting individual services. Clients often need to invoke multiple services, coordinated to reflect how those services interrelate and contribute to the overall application. Important examples include task allocation and event notification in collaborative workgroup systems, and task sequencing and routing in workflow applications. Failure to address control requirements for such interactions has impeded development of uniform methods and tools for building many types of distributed systems with client/server architectures. The article identifies and examines extensions to the basic client/server model that provide explicit support for coordinating multiserver interactions     

An incremental algorithm for generating all minimal models

The task of generating minimal models of a knowledge base is at the computational heart of diagnosis systems like truth maintenance systems, and of nonmonotonic systems like autoepistemic logic, default logic, and disjunctive logic programs. Unfortunately, it is NP-hard. In this paper we present a hierarchy of classes of knowledge bases, Ψ₁,Ψ₂,… , with the following properties: first, Ψ₁ is the class of all Horn knowledge bases; second, if a knowledge base T is in Ψk, then T has at most k minimal models, and all of them may be found in time O(lk²), where l is the length of the knowledge base; third, for an arbitrary knowledge base T, we can find the minimum k such that T belongs to Ψk in time polynomial in the size of T; and, last, where K is the class of all knowledge bases, it is the case that , that is, every knowledge base belongs to some class in the hierarchy. The algorithm is incremental, that is, it is capable of generating one model at a time.     

Complexity classes in models of cellular computing with membranes

In this paper we introduce four complexity classes for cellularcomputing systems with membranes: the first and the second ones containall decision problems solvable in polynomial time by a family ofdeterministic P systems, without and with an input membrane,respectively; the third and fourth classes contain all decision problemssolvable in polynomial time by a family of non-deterministic P systems,without and with an input membrane, respectively. We illustrate theusefulness of these classes by solving two NP–completeproblems, namely HPP and SAT, in both variants of Psystems.