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Fast and efficient contrast-enhanced super-resolution without real-world data using concatenated recursive compressor-decompressor network

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IET IMAGE PROCESSING 2019年第5期13卷 817-824页

作者： Choi, Jun-Myung Kang, Dong-Joong Pusan Natl Univ Sch Mech Engn Busan 46241 South Korea

The authors propose a novel model called concatenated recursive compressor-decompressor network (CRCDNet) for contrast-enhanced super-resolution. The characteristics of authors' model can be summarised as follows. First, a compression-decompression process reduces the computational complexity compared with the general fully convolutional model. Second, an internal/external skip-connection is used to preserve information of the preceding layers. Finally, by employing a recursive module, authors' model has a small number of parameters, yet is a deep and robust network. The authors apply authors' proposed network to license plate images. As a real application, license plates can provide important evidence for investigation of crimes and for security, but it is very difficult to collect the vast amounts of license plates required for analysis based on a data-driven approach. To solve this problem, the authors generated virtual datasets to train authors' model, while analysing the performance with real license plate datasets. Authors' method achieves better performance than the state-of-the-art models on license plate images.

关键词： learning (artificial intelligence) image sensors traffic engineering computing parallel algorithms image resolution object recognition data compression image enhancement computational complexity license plate datasets state-of-the-art models license plate images fast contrast-enhanced super-resolution efficient contrast-enhanced super-resolution real-world data concatenated recursive compressor-decompressor network compression-decompression process general fully convolutional model recursive module deep network robust network license plates internal-external skip-connection CRCDNet

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Computing automorphism groups of chordal graphs whose simplicial components are of small size

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IEICE TRANSACTIONS ON INFORMATION AND SYSTEMS 2006年第8期E89D卷 2388-2401页

作者： Toda, Seinosuke Nihon Univ Dept Comp Sci & Syst Anal Coll Humanities & Sci Tokyo 1568550 Japan

It is known that any chordal graph can be uniquely decomposed into simplicial components. Based on this fact, it is shown that for a given chordal graph, its automorphism group can be computed in O((c! - n)(O(1))) time, where c denotes the maximum size of simplicial components and n denotes the number of nodes. It is also shown that isomorphism of those chordal graphs can be decided within the same time bound. From the viewpoint of polynomial-time computability, our result strictly strengthens the previous ones respecting the clique number.

关键词： chordal graph simplicial component automorphism isomorphism computational group theory algorithm computational complexity

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Robust fast PMU measurement recovery enhanced by randomized singular value and sequential Tucker decomposition

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IET GENERATION TRANSMISSION & DISTRIBUTION 2022年第16期16卷 3267-3281页

作者： Pei, Jianhua Wang, Ziyu Wang, Jingyu Shi, Dongyuan Huazhong Univ Sci & Technol Sch Elect & Elect Engn Minist Educ Engn Res Ctr Power Safety & EfficiencyState Key Wuhan 430074 Peoples R China

The development of cyber-physical power systems raises concerns about the data quality issue of phasor measurement units (PMUs). Low signal-to-noise ratios (SNRs) and data losses caused by malicious electromagnetic interference, false data injections, and equipment malfunctioning may jeopardize the data integrity and availability necessary for power system monitoring, protection, and control. To ensure grid resiliency, this paper proposes a robust fast PMU measurement recovery (RFMR) algorithm based on improved singular spectrum analysis (SSA) of Hankel structures. It utilizes single or multiple channels of PMU time-series to restore the problematic phasor measurements with low-SNR noises and data losses. Additionally, the traditional singular value decomposition (SVD) and Tucker decomposition (TD) in RFMR are replaced by randomized SVD (RSVD) and sequential TD (STD) to reduce the computational complexity in single-channel and multi-channel RFMR, respectively. Numerical case studies demonstrate that the proposed algorithm can recover the noise-contaminated measurements with higher accuracy than existing methods, such as matrix/tensor decomposition approaches and robust principal component analysis (RPCA), and effectively complement the missing data with the observed measurements corrupted by low SNRs. Moreover, the latency margins of various power system synchrophasor application scenarios can be satisfied with the reduced computational complexity.

关键词： data quality issue missing data computational complexity observed measurements decomposition approaches randomized singular value cyber-physical systems data losses power system monitoring noise-contaminated measurements power system synchrophasor application scenarios PMU time-series grid resiliency improved singular spectrum analysis singular value decomposition principal component analysis equipment malfunctioning robust fast PMU measurement recovery algorithm problematic phasor measurements multichannel RFMR electromagnetic interference cyber-physical power systems phasor measurement tensors robust principal component analysis time series data integrity power system measurement false data injections low SNRs phasor measurement units power engineering computing malicious electromagnetic interference

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INTERACTIVE PROOF SYSTEMS AND ALTERNATING TIME-SPACE complexity

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THEORETICAL COMPUTER SCIENCE 1993年第1期113卷 55-73页

作者： FORTNOW, L LUND, C Department of Computer Science University of Chicago 1100 E. 58th Street Chicago IL 60637 USA

We show a rough equivalence between alternating time-space complexity and a public-coin interactive proof system with the verifier having a polynomial-related time-space complexity. Special cases include the following: All of NC has interactive proofs, with a log-space polynomial-time public-coin verifier vastly improving the best previous lower bound of LOGCFL for this model (Fortnow and Sipser, 1988). All languages in P have interactive proofs with a polynomial-time public-coin verifier using o(log2 n) space. All exponential-time languages have interactive proof systems with public-coin polynomial-space exponential-time verifiers. To achieve better bounds, we show how to reduce a k-tape alternating Turing machine to a 1-tape alternating Turing machine with only a constant factor increase in time and space.

关键词： computational complexity

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ELECTRONIC DATA SORTING

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IEEE TRANSACTIONS ON COMPUTERS 1985年第4期34卷 296-310页

作者： DEMUTH, HB Department of Electrical Engineering University of Tulsa Tulsa OK 7410 Abstract Authors References Cited By Keywords Metrics Similar Download Citation Email Print Request Permissions

This paper presents results of a study of the fundamentals of sorting. Emphasis is placed on understanding sorting and on minimizing the time required to sort with electronic equipment of reasonable cost. Sorting is viewed as a combination of information gathering and item moving activities. Shannon"s communication theory measure of information is applied to assess the difficulty of various sorting problems. Bounds on the number of comparisons required to sort are developed, and optimal or near-optimal sorting schemes are described and investigated. Three abstract sorting models based on cyclic, linear, and randomaccess memories are defined. Optimal or near-optimal sorting methods are developed for the models and their parallel-register extensions. A brief review of the origin of the work and some of its hypotheses is also presented.

关键词： Bounds communication theory comparisons complexity computational complexity information gathering information theory item moving model optimal parallel sorting

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POLYNOMIAL-TIME COMPUTATION OF HOMOTOPY GROUPS AND POSTNIKOV SYSTEMS IN FIXED DIMENSION

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SIAM JOURNAL ON COMPUTING 2014年第5期43卷 1728-1780页

作者： Cadek, Martin Krcal, Marek Matousek, Jiri Vokrinek, Lukas Wagner, Uli Masaryk Univ Dept Math & Stat CS-61137 Brno Czech Republic Charles Univ Prague Dept Appl Math CR-11800 Prague 1 Czech Republic ETH Dept Comp Sci CH-8092 Zurich Switzerland EPFL SB MATHGEOM Ecole Polytech Fed Lausanne Inst Math Geometrie & Applicat CH-1015 Lausanne Switzerland

For several computational problems in homotopy theory, we obtain algorithms with running time polynomial in the input size. In particular, for every fixed k >= 2, there is a polynomial-time algorithm that, for a 1-connected topological space X given as a finite simplicial complex, or more generally, as a simplicial set with polynomial-time homology, computes the kth homotopy group pi(k)(X), as well as the first k stages of a Postnikov system of X. Combined with results of an earlier paper, this yields a polynomial-time computation of [X, Y], i.e., all homotopy classes of continuous mappings X -> Y, under the assumption that Y is (k - 1)-connected and dim X <= 2k - 2. We also obtain a polynomial-time solution of the extension problem, where the input consists of finite simplicial complexes X -> Y, where Y is (k - 1)-connected and dim X <= 2k - 1, plus a subspace A subset of X and a (simplicial) map f : A -> Y, and the question is the extendability of f to all of X. The algorithms are based on the notion of a simplicial set with polynomial-time homology, which is an enhancement of the notion of a simplicial set with effective homology developed earlier by Sergeraert and his coworkers. Our polynomial-time algorithms are obtained by showing that simplicial sets with polynomial-time homology are closed under various operations, most notably Cartesian products, twisted Cartesian products, and classifying space. One of the key components is also polynomial-time homology for the Eilenberg-MacLane space K(Z, 1), provided in another recent paper by Krcal, Matousek, and Sergeraert.

关键词： algebraic topology homotopy theory homotopy groups Postnikov systems computational complexity

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Robust fast maximum likelihood with assumed clutter covariance algorithm for adaptive clutter suppression

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IET RADAR SONAR AND NAVIGATION 2014年第9期8卷 1184-1194页

作者： Tang, Bo Zhang, Yu Tang, Jun Inst Elect Engn Lab 504 Hefei 230037 Peoples R China Tsinghua Univ Dept Elect Engn Beijing 100084 Peoples R China

The mismatch between the clutter and noise power of the prior knowledge and true interference covariance matrix degrades the performance of fast maximum likelihood with assumed clutter covariance (FMLACC) algorithm significantly. By introducing a scale parameter to flexibly adjust the prior power, the authors propose an algorithm which is more robust to the power mismatch than FMLACC algorithm. They also develop a more straightforward method to derive the maximum likelihood covariance matrix estimator under this scaled knowledge constraint. Moreover, they study the problem of automatically determining the scale parameter. The authors provide two parameter selection methods, the first of which is based on estimating the minimum eigenvalue of the prewhitened sample covariance matrix, and the second is based on cross validation. To reduce the computational complexity, they also develop fast implementations for the parameter selection based on cross validation. Numerical simulations demonstrate the performance enhancement of the proposed algorithm compared with FMLACC algorithm in cases of mismatched prior knowledge.

关键词： space-time adaptive processing computational complexity covariance matrices eigenvalues and eigenfunctions numerical analysis maximum likelihood estimation radar clutter pulsed Doppler radar space-time adaptive processing performance enhancement numerical simulations parameter selection computational complexity covariance matrix eigenvalue parameter selection methods maximum likelihood covariance matrix estimator power mismatch FMLACC algorithm interference covariance matrix noise power adaptive clutter suppression clutter covariance algorithm robust fast maximum likelihood

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Hardness of approximating the Shortest Vector Problem in high l_p norms

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JOURNAL OF COMPUTER AND SYSTEM SCIENCES 2006年第2期72卷 206-219页

作者： Khot, S Princeton Univ Dept Comp Sci Princeton NJ 08544 USA

We present a new hardness of approximation result for the Shortest Vector Problem in l(P) norm (denoted by SVPp). Assuming NP not subset of ZPP, we show that for every epsilon > 0, there is a constant p(epsilon) such that for all integers p >= p(epsilon), the problem SVPp has no polynomial time approximation algorithm with approximation ratio p(1-epsilon). (c) 2005 Elsevier Inc. All rights reserved.

关键词： computational complexity lattices Shortest Vector Problem approximation algorithms hardness of approximation

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On limits on the computational power of data-accumulating algorithms

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INFORMATION PROCESSING LETTERS 2003年第4期86卷 221-227页

作者： Bruda, SD Akl, SG Bishops Univ Dept Comp Sci Lennoxville PQ J1M 1Z7 Canada Queens Univ Sch Comp Kingston ON K7L 3N6 Canada

In the data-accumulating paradigm, inputs arrive continuously in real time, and the computation terminates when all the already received data are processed before another datum arrives. Previous research states that a constant upper bound on the running time of a successful algorithm within this paradigm exists only for particular forms of the data arrival law. This contradicts our recent conjecture that those problems that are solvable in real time are included in the class of logarithmic space-bounded computations. However, we prove that such an upper bound does exist in fact in both the parallel and sequential cases and for any polynomial arrival law, thus strengthening the mentioned conjecture. Then, we analyze an example of a noncontinuous data arrival law. We find similar properties for the sorting algorithm under such a law, namely the existence of an upper bound on the running time, suggesting that such properties do not depend on the form of the arrival law. (C) 2003 Elsevier Science B.V. All rights reserved.

关键词： computational complexity data-accumulating algorithms sorting parallel algorithms

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Fast capacitor voltage balancing strategy based on system history operation information for MMC

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IET GENERATION TRANSMISSION & DISTRIBUTION 2019年第7期13卷 1104-1109页

作者： Wang, Qin Liu, Kaipei Wang, Kun Qin, Liang Zhang, Jian Pu, Qingxin Wuhan Univ Sch Elect Engn & Automat Wuhan 430072 Hubei Peoples R China State Grid Corp China Dept DC Construct Beijing 100031 Peoples R China Global Energy Interconnect Res Inst Co Ltd Intellectual Property Operat Ctr Beijing 102200 Peoples R China

The conventional capacitor voltage balancing strategy of the modular multi-level converter (MMC) requires real-time sorting in each control cycle, which brings huge computational load to the controller. Therefore, a fast capacitor voltage balancing method for MMC is proposed. Based on the conventional strategy, this method combines the operating rules of the sub-module (SM), considering the voltages of SMs and historical information on charging and discharging of the capacitor. It selects the appropriate insert object and insertion process according to the relationship between the number of the switched-on and switched-off SMs in the last control cycle, and quickly forms the ordered sequence of SMs in the control cycle. The simulation results show that the proposed strategy can achieve voltage balancing with low computational complexity, significantly improve the system simulation speed, and effectively reduce the controller resources occupied by the balancing strategy.

关键词： sorting voltage control capacitors computational complexity power convertors power capacitors MMC conventional capacitor voltage balancing strategy modular multilevel converter control cycle huge computational load fast capacitor voltage conventional strategy operating rules voltages SMs historical information appropriate insert object insertion process controller resources system history operation information

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