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Abrasive waterjet machining simulation by SPH method

INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY 2010年第1-4期50卷 227-234页

作者： Wang Jianming Gao Na Gong Wenjun Shandong Univ Sch Mech Engn Jinan 250061 Peoples R China

Abrasive waterjet machining (AWJM) is a non-conventional process. The mechanism of material removing in AWJM for ductile materials and existing erosion models are reviewed in this paper. To overcome the difficulties of fluid-solid interaction and extra-large deformation problem using finite element method (FEM), the SPH-coupled FEM modeling for abrasive waterjet machining simulation is presented, in which the abrasive waterjet is modeled by SPH particles and the target material is modeled by FE. The two parts interact through contact algorithm. The creativity of this model is multi-materials SPH particles, which contain abrasive and water and mix together uniformly. To build the model, a randomized algorithm is proposed. The material model for the abrasive is first presented. Utilizing this model, abrasive waterjet penetrating the target materials with high velocity is simulated and the mechanism of erosion is depicted. The relationship between the depth of penetration and jet parameters, including water pressure and traverse speed, etc., are analyzed based on the simulation. The results agree with the experimental data well. It will be a benefit to understand the abrasive waterjet cutting mechanism and optimize the operating parameters.

关键词： Abrasive waterjet machining (AWJM) randomized algorithm Coupling SPH/FEM Abrasive material models

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Estimation of horizontal and vertical translations of large images based on columns and rows mean energy matching

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MULTIDIMENSIONAL SYSTEMS AND SIGNAL PROCESSING 2014年第2期25卷 273-294页

作者： Skubalska-Rafajlowicz, Ewa Wroclaw Univ Technol Inst Comp Engn Automat & Robot PL-50370 Wroclaw Poland

In this paper mean energy lateral histograms have been developed and used for the translation of frames detection and for the estimation of a shift vector in large image frames. 2-D translation problem is solved by two almost independent 1-D problems based on the mean energy lateral histograms. We formulate a simple optimization for estimating vertical or horizontal translations of the frame. The optimization goal is to find the best match between energies (squared norms) of rows (columns) of the image and the reference frame. The shift estimate is calculated as the minimizer of the least squares, maximum deviation or the sum of absolute deviations criterion. However, the first criterion is preferred, the last two almost always gave the same results when the noise level is low. The proposed method is faster than the FFT based phase-correlation approach. An iterative version of the algorithm is presented which is very reliable and usually converges in at most two iterations. A randomized version of the method which reduce further the computational cost for large images problems is also proposed. Experimental results are provided and discussed.

关键词： Image stabilization Shift estimation randomized algorithm Lateral energy histograms

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A Novel Fiber Intrusion Signal Recognition Method for OFPS Based on SCN With Dropout

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JOURNAL OF LIGHTWAVE TECHNOLOGY 2019年第20期37卷 5221-5230页

作者： Li, Wei Zeng, Zhiqiang Qu, Hongquan Sun, Chengbin North China Univ Technol Sch Informat Sci & Technol Beijing 100144 Peoples R China

Accurate and fast recognition of fiber intrusion signals has always been a fundamental task in the Optical Fiber Pre-warning System (OFPS). However, currently existing recognition models tend to focus on one aspect and lack a comprehensive approach. In this paper, a dropout-based Stochastic Configuration Network (SCN) optical fiber intrusion signal recognition model is first proposed, which is named DropoutSCN. By combining dropout with randomized algorithm models, it not only enhances the fast learning ability, but also improves the generalization performance of the recognition model. In the experiment, compared with traditional Artificial Neural Network (ANN), Random Vector Functional Link (RVFL), and original SCN models, the DropoutSCN model proposed in this paper has the lowest rootmean-square error (RMSE). In terms of time efficiency, it reduces the time delay by about 2.5 times compared with the traditional ANN. In addition, this paper applies dropout to SCN, which provides a feasible thinking and reference for the study of randomized algorithm models.

关键词： Dropout optical fiber pre-warning system randomized algorithm signal recognition stochastic configuration network

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Pass-efficient truncated UTV for low-rank approximations

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COMPUTATIONAL & APPLIED MATHEMATICS 2024年第1期43卷 1-18页

作者： Ji, Ying Feng, Yuehua Dong, Yongxin Shanghai Univ Engn Sci Sch Math Phys & Stat Shanghai 201620 Peoples R China East China Univ Polit Sci & Law Sch Law & Criminal Justice Shanghai 201620 Peoples R China

We propose the pass-efficient truncated UTV algorithm, a faster variant of the TUXV algorithm for low-rank approximations. Compared with the TUXV algorithm, data transfer and the complexity of the proposed algorithm are reduced. Therefore, our algorithm is suitable for large matrices stored out of memory or generated by streaming data. We also develop residual error upper bounds and singular value approximation error bounds for the pass-efficient truncated UTV algorithm. Numerical experiments are reported to demonstrate the efficiency and effectiveness of our algorithm.

关键词： SVD randomized algorithm Low-rank approximation UTV factorization Pass-efficient

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A Property Tester for Tree-Likeness of Quartet Topologies

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THEORY OF COMPUTING SYSTEMS 2011年第3期49卷 576-587页

作者： Chang, Maw-Shang Lin, Chuang-Chieh Rossmanith, Peter Natl Chung Cheng Univ Dept Comp Sci & Informat Engn Chiayi 621 Taiwan Rhein Westfal TH Aachen Dept Comp Sci D-52056 Aachen Germany

Property testing is a rapid growing field in theoretical computer science. It considers the following task: given a function f over a domain D, a property P and a parameter 0 0, and present the first property tester ... 详细信息

Property testing is a rapid growing field in theoretical computer science. It considers the following task: given a function f over a domain D, a property P and a parameter 0 < epsilon < 1, by examining function values of f over o(vertical bar D vertical bar) elements in D, determine whether f satisfies P or differs from any one which satisfies P in at least epsilon vertical bar D vertical bar elements. An algorithm that fulfills this task is called a property tester. We focus on tree-likeness of quartet topologies, which is a combinatorial property originating from evolutionary tree construction. The input function is f(Q), which assigns one of the three possible topologies for every quartet over an n-taxon set S. We say that fQ satisfies tree-likeness if there exists an evolutionary tree T whose induced quartet topologies coincide with f(Q). In this paper, we prove the existence of a set of quartet topologies of error number at least c((n)(4)) for some constant c > 0, and present the first property tester for tree-likeness of quartet topologies. Our property tester makes at most O(n(3)/epsilon) queries, and is of one-sided error and non-adaptive.

关键词： randomized algorithm Property testing Evolutionary tree Quartet method

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ON THE POWER OF CHOICE FOR BOOLEAN FUNCTIONS

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SIAM JOURNAL ON DISCRETE MATHEMATICS 2022年第3期36卷 1943-1954页

作者： Fraiman, Nicolas Lichev, Lyuben Mitsche, Dieter Univ N Carolina Chapel Hill NC 27599 USA Univ Lyon 1 Inst Camille Jordan Lyon France Univ Jean Monnet St Etienne France

In this paper we consider a variant of the well-known Achlioptas process for graphs adapted to monotone Boolean functions. Fix a number of choices r is an element of N and a sequence of increasing functions (f(n))(n >= 1) such that, for every n >= 1, f(n) : {0, 1}(n) (sic) {0, 1}. Given n bits which are all initially equal to 0, at each step r 0-bits are sampled uniformly at random and are proposed to an agent. Then, the agent selects one of the proposed bits and turns it from 0 to 1 with the goal to reach f(n)(-1) (1) as quickly as possible. We nearly characterize the conditions on (f(n))(n >= 1) under which an acceleration by a factor of r(1+ o(1)) is possible and underline the wide applicability of our results by giving examples from the fields of Boolean functions and graph theory.

关键词： Boolean function power of choice threshold hitting probability relevant variable Achlioptas process randomized algorithm

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UTV decomposition of dual matrices and its applications

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COMPUTATIONAL & APPLIED MATHEMATICS 2024年第1期43卷 1-18页

作者： Xu, Renjie Wei, Tong Wei, Yimin Yan, Hong Fudan Univ Sch Math Sci Shanghai 200433 Peoples R China Fudan Univ Inst Sci & Technol Brain Inspired Intelligence Shanghai 200433 Peoples R China Fudan Univ Sch Math Sci Shanghai Key Lab Contemporary Appl Math Shanghai 200433 Peoples R China City Univ Hong Kong Ctr Intelligent Multidimens Data Anal Dept Elect Engn Hong Kong Peoples R China

Matrix factorization in the context of dual numbers has found applications, in recent years, in fields such as kinematics and computer graphics. In this paper, we develop an efficient approach for handling large-scale data low-rank approximation problems using the UTV decomposition of dual matrices (DUTV). Theoretically, we propose an explicit expression for the DUTV and provide necessary and sufficient conditions for its existence. During this process, we also discovered that the general low-rank model for dual matrices can be solved by the Sylvester equation. In numerical experiments, the DUTV algorithm outperforms the dual matrix SVD algorithm in terms of speed and maintains effective performance in wave recognition. Subsequently, we utilize the DUTV algorithm to validate brain functional circuits in large-scale task-state functional magnetic resonance imaging data. Successfully identifying three types of wave signals, the DUTV method provides substantial empirical evidence for cognitive neuroscience theories.

关键词： Dual matrices UTV decomposition Low-rank approximation randomized algorithm Traveling wave identification Brain dynamics

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Sequential function approximation with noisy data

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JOURNAL OF COMPUTATIONAL PHYSICS 2018年 371卷 363-381页

作者： Shin, Yeonjong Wu, Kailiang Xiu, Dongbin Ohio State Univ Dept Math 231 W 18th Ave Columbus OH 43210 USA

We present a sequential method for approximating an unknown function sequentially using random noisy samples. Unlike the traditional function approximation methods, the current method constructs the approximation using one sample at a time. This results in a simple numerical implementation using only vector operations and avoids the need to store the entire data set. The method is thus particularly suitable when data set is exceedingly large. Furthermore, we present a general theoretical framework to define and interpret the method. Both upper and lower bounds of the method are established for the expectation of the results. Numerical examples are provided to verify the theoretical findings. (C) 2018 Elsevier Inc. All rights reserved.

关键词： Approximation theory randomized algorithm Noisy data

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Memory optimal dispersion by anonymous mobile robots

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DISCRETE APPLIED MATHEMATICS 2023年第1期340卷 171-182页

作者： Das, Archak Bose, Kaustav Sau, Buddhadeb Jadavpur Univ Dept Math 188 Raja SC Mallick Rd Kolkata 700032 W Bengal India Indian Stat Inst Adv Comp & Microelect Unit 203 B T Rd Kolkata 700108 W Bengal India

Consider a team of kappa <= n autonomous mobile robots initially placed at a node of an arbitrary graph G with n nodes. The dispersion problem asks for a distributed algorithm that allows the robots to reach a configuration in which each robot is at a distinct node of the graph. If the robots are anonymous, i.e., they do not have any unique identifiers, then the problem is not solvable by any deterministic algorithm. However, the problem can be solved even by anonymous robots if each robot is given access to a fair coin which they can use to generate random bits. In this setting, it is known that the robots require O(log.) bits of memory to achieve dispersion, where. is the maximum degree of G. On the other hand, the best known memory upper bound is min{Delta,max{log Delta, log D}} (D = diameter of G), which can be omega(log Delta), depending on the values of Delta and D. In this paper, we close this gap by presenting an optimal algorithm requiring O(log Delta) bits of memory. (c) 2023 Elsevier B.V. All rights reserved.

关键词： Mobile robots Dispersion Depth first search Distributed algorithms randomized algorithm

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A new approach to the minimum cut problem

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JOURNAL OF THE ACM 1996年第4期43卷 601-640页

作者： Karger, DR Stein, C DARTMOUTH COLL HANOVER NH 03755 USA

This paper presents a new approach to finding minimum cuts in undirected graphs. The fundamental principle is simple: the edges in a graph's minimum cut form an extremely small fraction of the graph's edges. Using this idea, we give a randomized, strongly polynomial algorithm that finds the minimum cut in an arbitrarily weighted undirected graph with high probability. The algorithm runs in O(n(2)log(3)n) time, a significant improvement over the previous (O) over tilde(mn) time bounds based on maximum flows. It is simple and intuitive and uses no complex data structures. Our algorithm can be parallelized to run in RNC with n(2) processors;this gives the first proof that the minimum cut problem can be solved in RNC. The algorithm does more than find a single minimum cut;it finds all of them. With minor modifications, our algorithm solves two other problems of interest. Our algorithm finds all cuts with value within a multiplicative factor of cu of the minimum cut's in expected (O) over tilde(n(2 alpha)) time, or in RNC with n(2 alpha) processors. The problem of finding a minimum multiway cut of a graph into r pieces is solved in expected (O) over tilde(n(2(r-1))) time, or in RNC with n(2(r-1)) processors. The ''trace'' of the algorithm's execution on these two problems forms a new compact data structure for representing all small cuts and all multiway cuts in a graph. This data structure can be efficiently transformed into the more standard cactus representation for minimum cuts.

关键词： graph algorithm minimum cut network reliability parallel computing randomized algorithm

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