44819319
Parallelizable execution-driven simulation of threaded distributed memory parallel computations
Discrete-event simulation is an important tool used for the performance evaluation of parallel systems. The space of tradeoffs is large however, when attempting to balance model fidelity and simulation execution tame. The paper describes a simulator-TAPS (Threaded Application Parallel System Simulator)-that, in the context of threaded parallel computations, provides a spectrum of possibilities in this tradeoff space. TAPS is specifically designed to be parallelized; we discuss some crucial considerations regarding its parallelization.
14667493
Safe timestamps and large-scale modeling
The paper examines issues that recur in consideration of simulation time-stamps, in the context of building very large simulation models from components developed by different groups at different times. A key problem here is "safety", loosely defined to mean that unintended model behavior does not occur due to unpredictable behavior of timestamp generation and comparisons. We revisit the problems of timestamp format and simultaneity, and then turn to the new problem of timestamp interoperability. We describe how a C++ simulation kernel can support the concurrent evaluation of submodels that internally use heterogeneous timestamps, and evaluate the execution time costs of doing so. We find that use of a safe timestamp format that explicitly allows different time scales costs less than 10% over a stock 64-bit integer format, whereas support for completely heterogeneous timestamps can cost as much as 50% in execution speed.
640793
A component-based approach to modeling and simulating mixed-signal and hybrid systems
Systems with both continuous and discrete behaviors can be modeled using a mixed-signal style or a hybrid systems style. This article presents a component-based modeling and simulation framework that supports both modeling styles. The component framework, based on an actor metamodel, takes a hierarchical approach to manage heterogeneity in modeling complex systems. We describe how ordinary differential equations, discrete event systems, and finite-state machines can be built under this metamodel. A mixed-signal system is a hierarchical composition of continuous-time and discrete event models, and a hybrid system is a hierarchical composition of continuous-time and finite-state-machine models. Hierarchical composition and information hiding help build clean models and efficient execution engines. Simulation technologies, in particular, the interaction between a continuous-time ODE solving engine and various discrete simulation engines are discussed. A signal type system is introduced to schedule hybrid components inside a continuous-time environment. Breakpoints are used to control the numerical integration step sizes so that discrete events are handled properly. A "refiring" mechanism and a "rollback" mechanism are designed to manage continuous components inside a discrete event environment. The technologies are implemented in the Ptolemy II software environment. Examples are given to show the applications of this framework in mixed-signal and hybrid systems.
15418886
Progressive Principal Component Analysis
Principal Component Analysis (PCA) is a feature extraction approach directly based on a whole vector pattern and acquires a set of projections that can realize the best reconstruction for an original data in the mean squared error sense. In this paper, the progressive PCA (PrPCA) is proposed, which could progressively extract features from a set of given data with large dimensionality and the extracted features are subsequently applied to pattern recognition. Experiments on the FERET database show its face recognition performance is better than those based on both E(PC)2A and FLDA.
52848704
Efficient encoding for address buses with temporal redundancy for simultaneous area and energy reduction
Interconnect area and energy dissipation are critical factors in any system designed today. In this work, we present techniques to help reduce area/cost and energy dissipation of address buses with significant temporal redundancy. We describe two encoding techniques for such buses, called pattern adjuster (PA) encoding and dynamic charge/discharge encoding (DCDE), that use simple hardware and no extra bus lines for control signals. Results show that, using PA encoding, self energy reduces by 18-38%, coupling toggle energy by 19-96%, and coupling charge/discharge energy by 14-40%. In addition, with DCDE applied on top of PA, coupling charge/discharge energy reduces by up to 48%. Overall, up to 25% address bus energy savings can be obtained using our techniques compared to the energy dissipation of the original bus, with 26-79% reduction in the number of bus lines. Our techniques use very simple hardware and will have negligible encoding/decoding latencies that are much lower than those of low-power bus encoding schemes.
13217169
New Method for Constructing Isospectral Graphs
There exist several methods available to construct isospectral molecular graphs.l-1° Recently, M. RandiC and his co-workers proposed the ring enlargement process (vide infra) for constructing subspectral graphs.” This method can be also used to construct isospectral graphs; however, it may fail sometimes. For example, the isospectral pair 1, 2 can be enlarged to the isospectral graphs 3,4 shown in Figure 1, where the symbol ‘‘z” signifies an isospectral pair and “-” denotes the ring enlargement procedure. Eigenvalues of 3, 4 are divided into two parts, those in coincidence with that of 1 , 2 are listed on the left, and the remaining ones are put on the right. On the other hand, graph pairs 7, 8 and 9, 10 in Figure 2, yielded from isospectral pair 5, 6, are not isospectral. Noticing the difference of the spectrum of graphs XX, XX’ (by “XX, XX”’ we mean that they are generated from subgraph X in double size by the enlargement procedure, such as 7, 8 from 5; and 9, 10 from a), RandiC suggested that if XX, XX’ are bipartite, they should be isospectral, because all eigenvalues now occur in pairs and the difference between XX and XX’ disappears. Hence, he proposed a conjecture below. CONJECTURE: If graph X yields nonisomorphic bipartite enlargements XX, XX’, etc.; the derived graphs are not only superspectral to the parent graph X but are also mutually cospectral.
5220045
A study of the performance and parameter sensitivity of adaptive distributed caching
A self-organized approach to manage a distributed proxy system called Adaptive Distributed Caching (ADC) has been proposed previously [8]. We model each proxy as an autonomous agent that is equipped to decide how to deal with client requests using local information. Experimental results show that our ADC algorithm is able to compete with typical hashing-based approaches. This paper gives a full description of the self-organizing distributed algorithm, with a performance comparison based on hits and hops rate. Additional evaluation of the parameters caching-, multiple- and single-table size is also presented.