共查询到20条相似文献,搜索用时 15 毫秒
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In this paper, the Minimum Polynomial Extrapolation method (MPE) is used to accelerate the convergence of the Characteristic–Based–Split
(CBS) scheme for the numerical solution of steady state incompressible flows with heat transfer. The CBS scheme is a fractional
step method for the solution of the Navier–Stokes equations while the MPE method is a vector extrapolation method which transforms
the original sequence into another sequence converging to the same limit faster then the original one without the explicit
knowledge of the sequence generator. The developed algorithm is tested on a two-dimensional benchmark problem (buoyancy–driven
convection problem) where the Navier–Stokes equations are coupled with the temperature equation. The obtained results show
the feature of the extrapolation procedure to the CBS scheme and the reduction of the computational time of the simulation. 相似文献
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The recent advance of multicore architectures and the deployment of multiprocessors as the mainstream computing platforms have given rise to a new concurrent programming impetus. Software transactional memories (STM) are one of the most promising approaches to take up this challenge. The aim of a STM system is to discharge the application programmer from the management of synchronization when he/she has to write multiprocess programs. His/her task is to decompose his/her program into a set of sequential tasks that access shared objects, and to decompose each task in atomic units of computation. The management of the required synchronization is ensured by the associated STM system. This paper presents two existing STM systems, and a new one based on time-window mechanism. The paper, which focuses mainly on STM principles, has an introductory and survey flavor. 相似文献
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In this study, an adaptive fuzzy time series model for forecasting Taiwan’s tourism demand is proposed to further enhance the predicted accuracy. We first transfer fuzzy time series data to the fuzzy logic group, assign weights to each period, and then use the proposed adaptive fuzzy time series model for forecasting in which an enrollment forecasting values is applied to obtain the smallest forecasting error. Finally, an illustrated example for forecasting Taiwan’s tourism demand is used to verify the effectiveness of proposed model and confirmed the potential benefits of the proposed approach with a very small forecasting error MAPE and RMSE. 相似文献
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Andreas Bauer Martin Leucker Christian Schallhart Michael Tautschnig 《International Journal on Software Tools for Technology Transfer (STTT)》2010,12(1):23-37
This paper describes a method for combining “off-the-shelf” SAT and constraint solvers for building an efficient Satisfiability Modulo Theories (SMT) solver for a wide range of theories. Our method follows the abstraction/refinement approach to simplify the implementation
of custom SMT solvers. The expected performance penalty by not using an interweaved combination of SAT and theory solvers is reduced by generalising a Boolean solution of an SMT problem first via assigning don’t care to as many variables as possible. We then use the generalised solution to determine a thereby smaller constraint set to be
handed over to the constraint solver for a background theory. We show that for many benchmarks and real-world problems, this
optimisation results in considerably smaller and less complex constraint problems. The presented approach is particularly
useful for assembling a practically viable SMT solver quickly, when neither a suitable SMT solver nor a corresponding incremental
theory solver is available. We have implemented our approach in the ABsolver framework and applied the resulting solver successfully to an industrial case-study: the verification problems arising in
verifying an electronic car steering control system impose non-linear arithmetic constraints, which do not fall into the domain
of any other available solver. 相似文献
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It is well known that every investment carries a risk associated, and depending on the type of investment, it can be very risky; for instance, securities. However, Markowitz proposed a methodology to minimize the risk of a portfolio through securities diversification. The selection of the securities is a choice of the investor, who counts with several technical analyzes to estimate investment’s returns and risks. This paper presents an autoregressive exogenous (ARX) predictor model to provide the risk and return of some Brazilian securities – negotiated at the Brazilian stock market, BOVESPA – to select the best portfolio, herein understood as the one with minimum expected risk. The ARX predictor succeeded in predicting expected returns and risks of the securities, which resulted in an effective portfolio. Additionally the Markowitz theory was confirmed, showing that diversification reduces the risk of a portfolio. 相似文献
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We consider a relaxation of the quadratic assignment problem without the constraint on the number of objects assigned to a specific position. This problem is NP-hard in the general case. To solve the problem, we propose a polynomial algorithm with guaranteed posterior accuracy estimate; we distinguish a class of problems with special assignment cost functions where the algorithm is 2-approximate. We show that if the graph in question contains one simple loop, and the set of assignment positions is a metric space, the proposed algorithm is 2-approximate and guaranteed to be asymptotically exact. We conduct a computational experiment in order to analyze the algorithm’s errors and evaluate its accuracy. 相似文献
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Tuomas Kärnä Benjamin de Brye Olivier Gourgue Jonathan Lambrechts Richard Comblen Vincent Legat Eric Deleersnijder 《Computer Methods in Applied Mechanics and Engineering》2011,200(5-8):509-524
Resolving the shoreline undulation due to tidal excursion is a crucial part of modelling water flow in estuaries and coastal areas. Nevertheless, maintaining positive water column depth and numerical stability has proved out to be a very difficult task that requires special attention. In this paper we propose a novel wetting–drying method in which the position of the sea bed is allowed to fluctuate in drying areas. The method is implemented in a Discontinuous Galerkin Finite Element Model (DG-FEM). Unlike most methods in the literature our method is compatible with fully implicit time-marching schemes, thus reducing the overall computational cost significantly. Moreover, global and local mass conservation is guaranteed which is crucial for long-term environmental applications. In addition consistency with tracer equation is also ensured. The performance of the proposed method is demonstrated with a set of test cases as well as a real-world application to the Scheldt Estuary. Due to the implicit time integration, the computational cost in the Scheldt application is reduced by two orders of magnitude. Although a DG-FEM implementation is presented here, the wetting–drying method is applicable to a wide variety of shallow water models. 相似文献
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Traditional set associative caches are seriously prone to conflict misses. We propose an adapted new skewed associative architecture
as an attempt to alleviate this problem. It has already been shown that skewed associative caches can reduce the rate of conflict
misses by using different hash functions to index different banks. Building on this observation, we propose yet another approach
to further reduce the rate of conflict misses, nicknamed YAARC (Yet Another Approach to Reducing Conflicts) that uses different hash functions to index into a single bank. Mathematical modeling and simulation results are exploited
to evaluate the impact of YAARC on the rate of conflict misses. Mathematical analysis show the superiority of YAARC caches
over set and skewed associative caches from the conflict miss point of view. Simulations, using some benchmarks from SPEC
CPU2000 benchmark suit that former researchers have reported them as the best candidates for cache performance evaluation,
also show nearly 43% conflict miss rate improvement for the skewed associative cache over the set associative cache, and nearly
31% improvement for the YAARC cache over the skewed associative cache. This implies that YAARC caches considerably outperform
set and skewed associative caches from the conflict miss point of view. Since production of YAARC caches require a dispensable
amount of hardware overhead, they can be considered as a cost effective approach to minimize the rate of conflict misses.
相似文献
Behrouz ZolfaghariEmail: |
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Stefano Micheletti Simona Perotto Marianna Signorini 《Computers & Mathematics with Applications》2018,75(6):2134-2152
Quasi-static crack propagation in brittle materials is modeled via the Ambrosio–Tortorelli approximation. The crack is modeled by a smooth phase-field, defined on the whole computational domain. Since the crack is confined to a thin layer, the employment of anisotropic adapted grids is shown to be a really effective tool in containing computational costs. We extend the anisotropic error analysis, applied to the classical Ambrosio–Tortorelli approximation by Artina et al., to the generalized Ambrosio–Tortorelli functional, where a unified framework for several elasticity laws is dealt with as well as a non-convex fracture energy can be accommodated. After deriving an anisotropic a posteriori error estimator, we devise an algorithm which alternates optimization and mesh adaptation. Both anti-plane and plane-strain configurations are numerically checked. 相似文献
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Most conventional learning algorithms require both positive and negative training data for achieving accurate classification
results. However, the problem of learning classifiers from only positive data arises in many applications where negative data
are too costly, difficult to obtain, or not available at all. This paper describes a new machine learning approach, called
ILoNDF (Incremental data-driven Learning of Novelty Detector Filter). The approach is inspired by novelty detection theory
and its learning method, which typically requires only examples from one class to learn a model. One advantage of ILoNDF is
the ability of its generative learning to capture the intrinsic characteristics of the training data by continuously integrating
the information relating to the relative frequencies of the features of training data and their co-occurrence dependencies.
This makes ILoNDF rather stable and less sensitive to noisy features which may be present in the representation of the positive
data. In addition, ILoNDF does not require extensive computational resources since it operates on-line without repeated training,
and no parameters need to be tuned. In this study we mainly focus on the robustness of ILoNDF in dealing with high-dimensional
noisy data and we investigate the variation of its performance depending on the amount of data available for training. To
make our study comparable to previous studies, we investigate four common methods: PCA residuals, Hotelling’s T
2 test, an auto-associative neural network, and a one-class version of the SVM classifier (lately a favored method for one-class
classification). Experiments are conducted on two real-world text corpora: Reuters and WebKB. Results show that ILoNDF tends
to be more robust, is less affected by initial settings, and consistently outperforms the other methods. 相似文献
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Sequencing a single machine with due dates and deadlines: an ILP-based approach to solve very large instances 总被引:1,自引:0,他引:1
We consider the problem of minimizing the weighted number of tardy jobs on a single machine where each job is also subject to a deadline that cannot be violated. We propose an exact method based on a compact integer linear programming formulation of the problem and an effective reduction procedure that allows to solve to optimality instances with up to 30,000 jobs in size, and up to 50,000 jobs in size for the special deadline-free case. 相似文献
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This article presents a novel inverse dynamic calculation approach for a haptic device with pantograph parallel platform. This approach uses vector differential equations in kinematics analysis, hence deriving the explicit expressions of all links’ linear velocities, linear accelerations, angular velocities, and angular accelerations. In contrast to the regular influence coefficient method, the kinematics expressions presented herein avoid the large calculation load of matrix inverse operation, which is crucial to real-time computation. Kane’s equation is employed to establish the inverse dynamic calculation expression for the special architecture of hybrid series-parallel branch. The elements of velocity wrench of the top plate are chosen as the generalized velocities. After deriving the matrixes of partial linear velocity and partial angular velocity, the inverse dynamic equation in explicit form is obtained. Compared with the results calculated by ADAMS, the precision of this calculation approach is validated. Given that it is highly efficient and accurate, this approach is more suitable for real-time compute-torque control, especially for mechanisms with hybrid series-parallel branches. 相似文献
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We consider the method that computes the shape orientation as the direction α that maximises the integral of the length of projections, taken to the power of 2N, of all the straight line segments whose end points belong to the shape, to a line that has the slope α. We show that for N=1 such a definition of shape orientation is consistent with the shape orientation defined by the axis of the least second moment of inertia. For N>1 this is not the case, and consequently our new method can produce different results. As an additional benefit our approach leads to a new method for computation of the orientation of compound objects. 相似文献
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In practice, the clearances of joints in a great number of mechanical systems are well under control. In these cases, some
of the existing methods become unpractical because of the little differences in the order of magnitude between relative movements
and computational errors. Assuming that the effects of impacts are negligible, we proved that both locations and forces of
contacts in joints can be fully determined by parts of joint reaction forces. Based on this fact, a method particularly suited
for multibody systems possessing frictional joints with tiny clearances is presented. In order to improve the efficiency of
computation, recursive formulations are proposed based on the interactions between bodies. The proposed recursive formulations
can improve the computation of joint reaction forces. With the methodology presented in this paper, not only the motion of
bodies in a multibody system but also the details about the contacts in joints, such as forces of contacts and locations of
contact points, can be obtained. Even with the assumption of impact free, the instants of possible impacts can be detected
without relying upon any ambiguous parameters, as indicated by numerical examples in this paper. 相似文献
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《国际计算机数学杂志》2012,89(4):437-450
The SInsDelP system with single contextual insertion and (u, v)-contextual deletion was introduced by Murugan and Easwarakumar. In this paper we discuss an application of the SInsDelP system for the construction of fractal images. The fractal images considered are of self-similar types, such as Koch Snowflake, Anti-Koch Snowflake, Fractal Tree and Sierpinski Triangle. This is performed in two stages. A DNA sequence for the fractal image is generated first by a sequence of SInsDelP operations, and then the respective image is produced through the specialized recognition algorithm. 相似文献