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The obstacle-avoiding rectilinear Steiner minimal tree (OARSMT) problem is a fundamental problem in very large-scale integrated circuit physical design and can be reduced to the Steiner tree problem in graphs (GSTP), which can be solved by using three types of common methods: classic heuristics, local search algorithms, or computational intelligence algorithms. However, classic heuristics have poor solution qualities; local search algorithms easily fall into the problem of the local optimum; and the searching effects of the existing computational intelligence algorithms are poor for this problem. In order to improve the solution quality, we propose a novel discrete artificial bee colony algorithm for constructing an obstacle-avoiding rectilinear Steiner tree. We first generate the escape graph for the OARSMT problem. Then, we search for a near-optimal solution consisting of some edges of escape graph by using the discrete ABC algorithm. We apply a key-node neighborhood configuration for the local search strategy and introduce two local search operators. We then naturally use a key-node-based encoding scheme for representing the feasible solution and obtain a tight searching scope. We employ a modified classic heuristic as the encoder that can produce a feasible solution.Experiments conducted on both general GSTP and very large-scale integrated circuit instances reveal the superior performance of the proposed method in terms of the solution quality among the state-of-the-art algorithms.Keywords NP-complete problem Á Obstacle-avoiding rectilinear Steiner minimal tree problem Á Steiner tree problem in graphs Á Local search Á Artificial bee colony algorithm Á VLSI physical design 1 Introduction

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The study of spatial and temporal changes in precipitation patterns is important to agriculture and natural ecosystems. These changes can be described by some climate change indices. Because these indices often have skewed probability distributions, some common statistical procedures become either inappropriate or less powerful when they are applied to the indices. A nonparametric approach based on stochastic ordering is proposed, which does not make any assumption on the shape of the distribution. This approach is applied to the average length of the period between two adjacent precipitation days, which is called the average number of consecutive dry days (ACDD). This approach is shown to be able to reveal some patterns in precipitation that other approaches do not. Using daily precipitations at 756 stations in China from 1960 to 2015, this work compares the ACDDs in three periods, 1960–1965, 1985–1990, and 2010–2015 for each province in China. The results show that ACDD increases stochastically from the period 1960–1965 to either the period 1985–1990 or the period 2010–2015, or from the period 1985–1990 to the period 2010–2015 in all but three provinces in China.

Anomaly detection over HTTP traffic has attracted much attention in recent years, which plays a vital role in many domains. This paper proposes an efficient machine learning approach to detect anomalous HTTP traffic that addresses the problems of existing methods, such as data redundancy and high training complexity. This algorithm draws on natural language processing (NLP) technology, uses the Word2vec algorithm to deal with the semantic gap, and implements Term Frequency-Inverse Document Frequency (TF-IDF) weighted mapping of HTTP traffic to construct a low-dimensional paragraph vector representation to reduce training complexity. Then we employs boosting algorithm Light Gradient Boosting Machine (LightGBM) and Categorical Boosting (CatBoost) to build an efficient and accurate anomaly detection model. The proposed method is tested on some artificial data sets, such as HTTP DATASET CSIC 2010, UNSW-NB15, and Malicious-URLs. Experimental results reveal that both the boosting algorithms have high detection accuracy, high true positive rate, and low false positive rate. Compared with other anomaly detection methods, the proposed algorithms require relatively short running time and low CPU memory consumption.