scholarly journals Uncovering Specific-Shape Graph Anomalies in Attributed Graphs

2019 ◽  
Vol 33 ◽  
pp. 5433-5440 ◽  
Author(s):  
Nannan Wu ◽  
Wenjun Wang ◽  
Feng Chen ◽  
Jianxin Li ◽  
Bo Li ◽  
...  
Keyword(s):  
Broad Class ◽  
Optimal Solution ◽  
Cost Functions ◽  
Shape Priors ◽  
Nonlinear Approach ◽  
Attributed Graphs ◽  
Specific Shape ◽  
Geometrical Convergence ◽  
Traditional Approaches ◽  
Modern Era

As networks are ubiquitous in the modern era, point anomalies have been changed to graph anomalies in terms of anomaly shapes. However, the specific-shape priors about anomalous subgraphs of interest are seldom considered by the traditional approaches when detecting the subgraphs in attributed graphs (e.g., computer networks, Bitcoin networks, and etc.). This paper proposes a nonlinear approach to specific-shape graph anomaly detection. The nonlinear approach focuses on optimizing a broad class of nonlinear cost functions via specific-shape constraints in attributed graphs. Our approach can be used to many different graph anomaly settings. The traditional approaches can only support linear cost functions (e.g., an aggregation function for the summation of node weights). However, our approach can employ more powerful nonlinear cost functions, and enjoys a rigorous theoretical guarantee on the near-optimal solution with the geometrical convergence rate.

scholarly journals Query-Driven Discovery of Anomalous Subgraphs in Attributed Graphs

2017 ◽  
Author(s):  
Nannan Wu ◽  
Feng Chen ◽  
Jianxin Li ◽  
Jinpeng Huai ◽  
Bo Li
Keyword(s):  
State Of The Art ◽  
Nonlinear Function ◽  
Optimal Solution ◽  
Scan Statistics ◽  
Detection Problem ◽  
Query Graph ◽  
Attributed Graphs ◽  
Connected Subgraphs ◽  
Traditional Approaches

For a detection problem, a user often has some prior knowledge about the structure-specific subgraphs of interest, but few traditional approaches are capable of employing this knowledge. The main technical challenge is that few approaches can efficiently model the space of connected subgraphs that are isomorphic to a query graph. We present a novel, efficient approach for optimizing a generic nonlinear cost function subject to a query-specific structural constraint. Our approach enjoys strong theoretical guarantees on the convergence of a nearly optimal solution and a low time complexity. For the case study, we specialize the nonlinear function to several well-known graph scan statistics for anomalous subgraph discovery. Empirical evidence demonstrates that our method is superior to state-of-the-art methods in several real-world anomaly detection tasks.

Iterated shape-bias graph cut with application to ellipse segmentation

2021 ◽  
Vol 40 (1) ◽  
pp. 53-63
Author(s):  
Xin Sun ◽  
Dong Li ◽  
Wei Wang ◽  
Hongxun Yao ◽  
Dongliang Xu ◽  
...  
Keyword(s):  
Graph Cut ◽  
Joint Estimation ◽  
Shape Priors ◽  
Object Shape ◽  
Shape Bias ◽  
Local Measurements ◽  
Specific Shape ◽  
Optimal Segmentation ◽  
Local Edge ◽  
Global And Local

 We present a novel graph cut method for iterated segmentation of objects with specific shape bias (SBGC). In contrast with conventional graph cut models which emphasize the regional appearance only, the proposed SBGC takes the shape preference of the interested object into account to drive the segmentation. Therefore, the SBGC can ensure a more accurate convergence to the interested object even in complicated conditions where the appearance cues are inadequate for object/background discrimination. In particular, we firstly evaluate the segmentation by simultaneously considering its global shape and local edge consistencies with the object shape priors. Then these two cues are formulated into a graph cut framework to seek the optimal segmentation that maximizing both of the global and local measurements. By iteratively implementing the optimization, the proposed SBGC can achieve joint estimation of the optimal segmentation and the most likely object shape encoded by the shape priors, and eventually converge to the candidate result with maximum consistency between these two estimations. Finally, we take the ellipse shape objects with various segmentation challenges as examples for evaluation. Competitive results compared with state-of-the-art methods validate the effectiveness of the technique.

Module-Based Static Structural Design of a Modular Reconfigurable Robot

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
Richard Phillip Mohamed ◽  
Fengfeng (Jeff) Xi ◽  
Allan Daniel Finistauri
Keyword(s):  
Structural Design ◽  
Design Method ◽  
Optimal Solution ◽  
Local Deformation ◽  
Design Stage ◽  
Coordinate Frame ◽  
Reconfigurable Robots ◽  
Nonlinear Approach ◽  
Reconfigurable Robot

In this paper, the structural design of modular reconfigurable robots (MRRs) is studied. This problem is defined as the determination of proper module sizes according to the robot’s payload and end-effector deflection specifications. Because an MRR has multiple configurations, a simple design process is proposed in order to avoid performing the structural design stage at each configuration. The final structural design is only carried out at a single configuration that can guarantee the robot’s satisfactory performance for all remaining feasible configurations. It is shown that the module structural design stage can be performed at the local coordinate frame of each module. While the module local force requirement can be fully determined, the determination of the module local deformation requirement is redundant. Thus, there can exist multiple design solutions. To overcome this problem, a nonlinear approach using a genetic algorithm is used to search for an optimal solution. Finally, a design simulation is performed on an example MRR, and the results show the effectiveness of the proposed design method.

scholarly journals Hidden invariant convexity for global and conic-intersection optimality guarantees in discrete-time optimal control

2021 ◽  
Author(s):  
Jorn H. Baayen ◽  
Krzysztof Postek
Keyword(s):  
Optimal Control ◽  
Power Systems ◽  
Discrete Time ◽  
Broad Class ◽  
Optimal Solution ◽  
Time Optimal Control ◽  
Exact Nature ◽  
State Variables ◽  
Numerical Experience ◽  
Time Optimal

AbstractNon-convex discrete-time optimal control problems in, e.g., water or power systems, typically involve a large number of variables related through nonlinear equality constraints. The ideal goal is to find a globally optimal solution, and numerical experience indicates that algorithms aiming for Karush–Kuhn–Tucker points often find solutions that are indistinguishable from global optima. In our paper, we provide a theoretical underpinning for this phenomenon, showing that on a broad class of problems the objective can be shown to be an invariant convex function (invex function) of the control decision variables when state variables are eliminated using implicit function theory. In this way, optimality guarantees can be obtained, the exact nature of which depends on the position of the solution within the feasible set. In a numerical example, we show how high-quality solutions are obtained with local search for a river control problem where invexity holds.

Venoms and poisonings during the centuries. A narrative review.

2020 ◽  
Vol 20 ◽  
Author(s):  
Ioannis Alexandros Charitos ◽  
Roberto Gagliano-Candela ◽  
Luigi Santacroce ◽  
Lucrezia Bottalico
Keyword(s):  
Roman Empire ◽  
19Th Century ◽  
Optimal Solution ◽  
Ancient Greece ◽  
Narrative Review ◽  
History Of ◽  
The 19Th Century ◽  
Modern Era ◽  
The Invisible

: Suffice it to say that the first traces of its use by man date back to ten thousand years ago the venom or poison since the last period of the Paleolithic man used poison to hunt and for defence. Indeed, in the second half of the 19th century, was found in some caves arrows made from the bones of animals characterized by particular grooves. In ancient Greece, the term pharmakon (φάρμακον) had a double meaning: remedy for therapy and venom. This is the period in which we become aware of the fact that a poison cannot be defined only as a substance capable of changing the properties of things. The poisonings are very frequent in the history of the Roman Empire and later in the Renaissance and the modern era. Poison was the protagonist political intrigues of power and is one of the most used lethal weapons over the years. Optimal solution for a perfect murder, the poison has a long history. Its success is due to the invisible and often unpunished death.

‘Celts: art and identity’ exhibition: ‘New Celticism’ at the British Museum

Antiquity ◽  
2016 ◽  
Vol 90 (349) ◽  
pp. 237-244 ◽  
Author(s):  
Manuel Fernández-Götz
Keyword(s):  
British Museum ◽  
Ongoing Debate ◽  
Modern Times ◽  
Ancient People ◽  
Celtic Languages ◽  
Traditional Approaches ◽  
The Relationship ◽  
Modern Era ◽  
Different Sources

Controversies about the ‘Celts’ have constituted an ongoing debate over the last few decades, with postures ranging from blank scepticism and denial, to critical revisions, but also to the maintenance of more traditional approaches. After a lively and overall useful debate in the pages of Antiquity between 1996–1998 (principally with articles by Vincent and Ruth Megaw vs Simon James and John Collis), Simon James's controversial volume The Atlantic Celts. Ancient people or modern invention? (1999) attracted considerable attention, both among scholars and the wider public, encouraging discussions about the relationship—if any—between modern Celtic identities and the ancient Celts. A major milestone was reached with the publication of John Collis's monograph The Celts. Origins, myths and inventions (2003), which is probably the best historiographical review about the construction of the concept and the different sources involved from Antiquity to modern times. One of his main points is that classical sources never referred to the presence of Celts on the British Isles and that the use of the term for the populations of ancient Britain was mainly an invention of the modern era (see also Morse 2005, How the Celts came to Britain). From a rather different perspective, new approaches based mostly on linguistics emphasise the crucial role of the Atlantic façade in the development of Celtic languages (Cunliffe & Koch 2010).

scholarly journals An Optimal Solution for Smooth and Non-Smooth Cost Functions-Based Economic Dispatch Problem

Energies ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3721 ◽  
Author(s):  
Chun-Yao Lee ◽  
Maickel Tuegeh
Keyword(s):  
Particle Swarm Optimization ◽  
Economic Dispatch ◽  
Logistic Map ◽  
Particle Swarm ◽  
Stable Solution ◽  
Optimal Solution ◽  
Cost Functions ◽  
Swarm Optimization ◽  
Chaotic Search ◽  
Modified Particle Swarm Optimization

A modified particle swarm optimization and incorporated chaotic search to solve economic dispatch problems for smooth and non-smooth cost functions, considering prohibited operating zones and valve-point effects is proposed in this paper. An inertia weight modification of particle swarm optimization is introduced to enhance algorithm performance and generate optimal solutions with stable solution accuracy and offers faster convergence characteristic. Moreover, an incorporation of chaotic search, called logistic map, is used to increase the global searching capability. To demonstrate the effectiveness and feasibility of the proposed algorithm compared to the several existing methods in the literature, five systems with different criteria are verified. The results show the excellent performance of the proposed method to solve economic dispatch problems.

A new type of multilevel system for image sparse recovery

2019 ◽  
Vol 17 (06) ◽  
pp. 1950049
Author(s):  
Guomin Sun ◽  
Jinsong Leng ◽  
Carlo Cattani
Keyword(s):  
Energy Distribution ◽  
Optimal Solution ◽  
Tight Frame ◽  
Sparse Recovery ◽  
Multilevel System ◽  
Convex Model ◽  
Generalized Gradient ◽  
Split Bregman ◽  
New Type ◽  
Specific Shape

This work focuses on image sparse recovery problem. First, we construct a new kind of pseudo-directional multilevel system, which forms a tight frame in [Formula: see text]. Different from the widely used directional multilevel transforms curvelts and shearlets, whose subbands are neat and nonsensitive to the energy distribution of signals in Fourier domain, the proposed multilevel system is designed to have subbands with specific shape, the shape is oriented by the energy distribution. Thus, we can obtain more sparse structure of signals and low computation for the multilevel transform. Moreover, to detect directional singularities of signals effectively, a local directional gradient operator is introduced to catch the signal variation along different directions, it can be seen as the generalized gradient. Then we proposed a simple but efficient method for image sparse recovery, the split Bregman algorithm is employed to solve the proposed convex model which guarantees the global optimal solution. Some contrast experiments suggest that the sparse recovery by the proposed method performs well in artifacts’ suppressing and details’ extraction.

scholarly journals A Test Score-Based Approach to Stochastic Submodular Optimization

2020 ◽  
Author(s):  
Shreyas Sekar ◽  
Milan Vojnovic ◽  
Se-Young Yun
Keyword(s):  
Test Scores ◽  
Test Score ◽  
Large Scale ◽  
Broad Class ◽  
Optimal Solution ◽  
Individual Performance ◽  
Constant Factor ◽  
Maximization Problem ◽  
Cardinality Constraint ◽  
Submodular Optimization

We study the canonical problem of maximizing a stochastic submodular function subject to a cardinality constraint, where the goal is to select a subset from a ground set of items with uncertain individual performances to maximize their expected group value. Although near-optimal algorithms have been proposed for this problem, practical concerns regarding scalability, compatibility with distributed implementation, and expensive oracle queries persist in large-scale applications. Motivated by online platforms that rely on individual item scores for content recommendation and team selection, we study a special class of algorithms that select items based solely on individual performance measures known as test scores. The central contribution of this work is a novel and systematic framework for designing test score–based algorithms for a broad class of naturally occurring utility functions. We introduce a new scoring mechanism that we refer to as replication test scores and prove that as long as the objective function satisfies a diminishing-returns condition, one can leverage these scores to compute solutions that are within a constant factor of the optimum. We then extend these scoring mechanisms to the more general stochastic submodular welfare-maximization problem, where the goal is to partition items into groups to maximize the sum of the expected group values. For this more difficult problem, we show that replication test scores can be used to develop an algorithm that approximates the optimal solution up to a logarithmic factor. The techniques presented in this work bridge the gap between the rigorous theoretical work on submodular optimization and simple, scalable heuristics that are useful in certain domains. In particular, our results establish that in many applications involving the selection and assignment of items, one can design algorithms that are intuitive and practically relevant with only a small loss in performance compared with the state-of-the-art approaches. This paper was accepted by Chung Piaw Teo, optimization.

GRADUATED ASSIGNMENT ALGORITHM FOR MULTIPLE GRAPH MATCHING BASED ON A COMMON LABELING

2013 ◽  
Vol 27 (01) ◽  
pp. 1350001 ◽  
Author(s):  
ALBERT SOLÉ-RIBALTA ◽  
FRANCESC SERRATOSA
Keyword(s):  
Graph Matching ◽  
Computational Cost ◽  
Optimal Solution ◽  
Structural Representation ◽  
Matching Problems ◽  
Assignment Algorithm ◽  
Attributed Graphs ◽  
The Common ◽  
Np Complete ◽  
Multiple Graph

In pattern recognition applications, with the aim of increasing efficiency, it is useful to represent the elements by attributed graphs (which consider their structural properties). Under this structural representation of the elements some graph matching problems need a common labeling between the vertices of a set of graphs. Computing this common labeling is a NP-Complete problem. Nevertheless, some methodologies have been presented which obtain a sub-optimal solution in polynomial time. The drawback of these methods is that they rely on pairwise labeling computations, causing the methodologies not to consider the global information during the entire process. To solve this problem, we present a methodology which generates the common labeling by matching all graph nodes to a virtual node set. The method has been tested using three independent datasets, one synthetic and two real. Experimental results show that the presented method obtains better performance than the most popular common labeling algorithm with the same computational cost.

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