Greedy optimization classifiers ensemble based on diversity

Decreasing the individual error and increasing the diversity among classifiers are two crucial factors for improving ensemble performances. Nevertheless, the “kappa-error” diagram shows that enhancing the diversity is at the expense of reducing individual accuracy. Hence, a new method named Matching Pursuit Optimization Ensemble Classifiers (MPOEC) is proposed in this paper in order to balance the diversity and the individual accuracy. MPOEC method adopts a greedy iterative algorithm of matching pursuit to search for an optimal combination of entire classifiers, and eliminates some similar or poor classifiers by giving zero coefficients. In MPOEC approach, the coefficient of every classifier is gained by minimizing the residual between the target function and the linear combination of the basis functions, especially, when the basis functions are similar, their coefficients will be close to zeros in one iteration of the optimization process, which indicates that obtained coefficients of classifiers are based on the diversity among ensemble individuals. Because some classifiers are given zero coefficients, MPOEC approach may be also considered as a selective classifiers ensemble method. Experimental results show that MPOEC improves the performance compared with other methods. Furthermore, the kappa-error diagrams indicate that the diversity is increased by the proposed method compared with standard ensemble strategies and evolutionary ensemble.     

Sparse ensembles using weighted combination methods based on linear programming

An ensemble of multiple classifiers is widely considered to be an effective technique for improving accuracy and stability of a single classifier. This paper proposes a framework of sparse ensembles and deals with new linear weighted combination methods for sparse ensembles. Sparse ensemble is to sparsely combine the outputs of multiple classifiers by using a sparse weight vector. When the continuous outputs of multiple classifiers are provided in our methods, the problem of solving sparse weight vector can be formulated as linear programming problems in which the hinge loss or/and the 1-norm regularization are exploited. Both the hinge loss and the 1-norm regularization are techniques inducing sparsity used in machine learning. We only ensemble classifiers with nonzero weight coefficients. In these LP-based methods, the ensemble training error is minimized while the weight vector of ensemble learning is controlled, which can be thought as implementing the structure risk minimization rule and naturally explains good performance of these methods. The promising experimental results over UCI data sets and the radar high-resolution range profile data are presented.     

A variant of Rotation Forest for constructing ensemble classifiers

Rotation Forest, an effective ensemble classifier generation technique, works by using principal component analysis (PCA) to rotate the original feature axes so that different training sets for learning base classifiers can be formed. This paper presents a variant of Rotation Forest, which can be viewed as a combination of Bagging and Rotation Forest. Bagging is used here to inject more randomness into Rotation Forest in order to increase the diversity among the ensemble membership. The experiments conducted with 33 benchmark classification data sets available from the UCI repository, among which a classification tree is adopted as the base learning algorithm, demonstrate that the proposed method generally produces ensemble classifiers with lower error than Bagging, AdaBoost and Rotation Forest. The bias–variance analysis of error performance shows that the proposed method improves the prediction error of a single classifier by reducing much more variance term than the other considered ensemble procedures. Furthermore, the results computed on the data sets with artificial classification noise indicate that the new method is more robust to noise and kappa-error diagrams are employed to investigate the diversity–accuracy patterns of the ensemble classifiers.     

EUSBoost: Enhancing ensembles for highly imbalanced data-sets by evolutionary undersampling

Classification with imbalanced data-sets has become one of the most challenging problems in Data Mining. Being one class much more represented than the other produces undesirable effects in both the learning and classification processes, mainly regarding the minority class. Such a problem needs accurate tools to be undertaken; lately, ensembles of classifiers have emerged as a possible solution. Among ensemble proposals, the combination of Bagging and Boosting with preprocessing techniques has proved its ability to enhance the classification of the minority class.In this paper, we develop a new ensemble construction algorithm (EUSBoost) based on RUSBoost, one of the simplest and most accurate ensemble, which combines random undersampling with Boosting algorithm. Our methodology aims to improve the existing proposals enhancing the performance of the base classifiers by the usage of the evolutionary undersampling approach. Besides, we promote diversity favoring the usage of different subsets of majority class instances to train each base classifier. Centered on two-class highly imbalanced problems, we will prove, supported by the proper statistical analysis, that EUSBoost is able to outperform the state-of-the-art methods based on ensembles. We will also analyze its advantages using kappa-error diagrams, which we adapt to the imbalanced scenario.     

基于概率校准的集成学习

针对原有集成学习多样性不足而导致的集成效果不够显著的问题,提出一种基于概率校准的集成学习方法以及两种降低多重共线性影响的方法。首先,通过使用不同的概率校准方法对原始分类器给出的概率进行校准;然后使用前一步生成的若干校准后的概率进行学习,从而预测最终结果。第一步中使用的不同概率校准方法为第二步的集成学习提供了更强的多样性。接下来,针对校准概率与原始概率之间的多重共线性问题,提出了选择最优(choose-best)和有放回抽样(bootstrap)的方法。选择最优方法对每个基分类器,从原始分类器和若干校准分类器之间选择最优的进行集成;有放回抽样方法则从整个基分类器集合中进行有放回的抽样,然后对抽样出来的分类器进行集成。实验表明,简单的概率校准集成学习对学习效果的提高有限,而使用了选择最优和有放回抽样方法后,学习效果得到了较大的提高。此结果说明,概率校准为集成学习提供了更强的多样性,其伴随的多重共线性问题可以通过抽样等方法有效地解决。     

A self-trained ensemble with semisupervised SVM: An application to pixel classification of remote sensing imagery

In this article, we present a semisupervised support vector machine that uses self-training approach. We then construct an ensemble of semisupervised SVM classifiers to address the problem of pixel classification of remote sensing images. Semisupervised support vector machines (S³VMs) are based on applying the margin maximization principle to both labeled and unlabeled samples. The ensemble of SVM classifiers recognizes the conceptual similarity between component classifiers from the same data source. The effectiveness of the proposed technique is first demonstrated for two numeric remote sensing data described in terms of feature vectors and then identifying different land cover regions in remote sensing imagery. Experimental results on these datasets show that employing this learning scheme can increase the accuracy level. The performance of the ensemble is compared with one of its component classifier and conventional SVM in terms of accuracy and quantitative cluster validity indices.     

Convex ensemble learning with sparsity and diversity

Classifier ensemble has been broadly studied in two prevalent directions, i.e., to diversely generate classifier components, and to sparsely combine multiple classifiers. While most current approaches are emphasized on either sparsity or diversity only, we investigate classifier ensemble focused on both in this paper. We formulate the classifier ensemble problem with the sparsity and diversity learning in a general mathematical framework, which proves beneficial for grouping classifiers. In particular, derived from the error-ambiguity decomposition, we design a convex ensemble diversity measure. Consequently, accuracy loss, sparseness regularization, and diversity measure can be balanced and combined in a convex quadratic programming problem. We prove that the final convex optimization leads to a closed-form solution, making it very appealing for real ensemble learning problems. We compare our proposed novel method with other conventional ensemble methods such as Bagging, least squares combination, sparsity learning, and AdaBoost, extensively on a variety of UCI benchmark data sets and the Pascal Large Scale Learning Challenge 2008 webspam data. Experimental results confirm that our approach has very promising performance.     

Compressive Image Reconstruction in Reduced Union of Subspaces

We present a new compressed sensing framework for reconstruction of incomplete and possibly noisy images and their higher dimensional variants, e.g. animations and light‐fields. The algorithm relies on a learning‐based basis representation. We train an ensemble of intrinsically two‐dimensional (2D) dictionaries that operate locally on a set of 2D patches extracted from the input data. We show that one can convert the problem of 2D sparse signal recovery to an equivalent 1D form, enabling us to utilize a large family of sparse solvers. The proposed framework represents the input signals in a reduced union of subspaces model, while allowing sparsity in each subspace. Such a model leads to a much more sparse representation than widely used methods such as K‐SVD. To evaluate our method, we apply it to three different scenarios where the signal dimensionality varies from 2D (images) to 3D (animations) and 4D (light‐fields). We show that our method outperforms state‐of‐the‐art algorithms in computer graphics and image processing literature.     

流形距离与压缩感知核稀疏投影的局部线性嵌入算法

流形学习算法的目的是发现嵌入在高维数据空间中的低维表示,现有的流形学习算法对邻域参数k和噪声比较敏感。针对此问题,文中提出一种流形距离与压缩感知核稀疏投影的局部线性嵌入算法,其核心思想是集成局部线性嵌入算法对高维流形结构数据的降维有效性与压缩感知核稀疏投影的强鉴别性,以实现高效有降噪流形学习。首先,在选择各样本点的近邻域时,采用流形距离代替欧氏距离度量数据间相似度的方法,创建能够正确反映流形内部结构的邻域图,解决以欧氏距离作为相似性度量时对邻域参数的敏感。其次,利用压缩感知核稀疏投影作为从高维观测空间到低维嵌入空间的映射,增强算法的鉴别性。最后,利用Matlab工具对实验数据集进行仿真,进一步验证所提算法的有效性。     

融入差异性的帕累托集成剪枝方法

相比于集成学习,集成剪枝方法是在多个分类器中搜索最优子集从而改善分类器的泛化性能,简化集成过程。帕累托集成剪枝方法同时考虑了分类器的精准度及集成规模两个方面,并将二者均作为优化的目标。然而帕累托集成剪枝算法只考虑了基分类器的精准度与集成规模,忽视了分类器之间的差异性,从而导致了分类器之间的相似度比较大。本文提出了融入差异性的帕累托集成剪枝算法,该算法将分类器的差异性与精准度综合为第1个优化目标,将集成规模作为第2个优化目标,从而实现多目标优化。实验表明,当该改进的集成剪枝算法与帕累托集成剪枝算法在集成规模相当的前提下,由于差异性的融入该改进算法能够获得较好的性能。     

基于随机子空间核极端学习机集成的高光谱遥感图像分类

结合随机子空间和核极端学习机集成提出了一种新的高光谱遥感图像分类方法。首先利用随机子空间方法从高光谱遥感图像数据的整体特征中随机生成多个大小相同的特征子集;然后利用核极端学习机在这些特征子集上进行训练从而获得基分类器;最后将所有基分类器的输出集成起来,通过投票机制得到分类结果。在高光谱遥感图像数据集上的实验结果表明:所提方法能够提高分类效果,且其分类总精度要高于核极端学习机和随机森林方法。     

一种新的基于多样性赋权证据推理的集成学习方法

在集成学习中使用平均法、投票法作为结合策略无法充分利用基分类器的有效信息,且根据波动性设置基分类器的权重不精确、不恰当。以上问题会降低集成学习的效果,为了进一步提高集成学习的性能,提出将证据推理(evidence reasoning, ER)规则作为结合策略,并使用多样性赋权法设置基分类器的权重。首先,由多个深度学习模型作为基分类器、ER规则作为结合策略,构建集成学习的基本结构;然后,通过多样性度量方法计算每个基分类器相对于其他基分类器的差异性;最后,将差异性归一化实现基分类器的权重设置。通过多个图像数据集的分类实验,结果表明提出的方法较实验选取的其他方法准确率更高且更稳定,证明了该方法可以充分利用基分类器的有效信息,且多样性赋权法更精确。     

An Evolutionary Algorithm Approach to Optimal Ensemble Classifiers for DNA Microarray Data Analysis

In general, the analysis of microarray data requires two steps: feature selection and classification. From a variety of feature selection methods and classifiers, it is difficult to find optimal ensembles composed of any feature-classifier pairs. This paper proposes a novel method based on the evolutionary algorithm (EA) to form sophisticated ensembles of features and classifiers that can be used to obtain high classification performance. In spite of the exponential number of possible ensembles of individual feature-classifier pairs, an EA can produce the best ensemble in a reasonable amount of time. The chromosome is encoded with real values to decide the weight for each feature-classifier pair in an ensemble. Experimental results with two well-known microarray datasets in terms of time and classification rate indicate that the proposed method produces ensembles that are superior to individual classifiers, as well as other ensembles optimized by random and greedy strategies.     

基于集成学习理论的文本情感分类

随着Web2.0的迅速发展,越来越多的用户乐于在互联网上分享自己的观点或体验。这类评论信息迅速膨胀,仅靠人工的方法难以应对网上海量信息的收集和处理,因此基于计算机的文本情感分类技术应运而生,并且研究的重点之一就是提高分类的精度。由于集成学习理论是提高分类精度的一种有效途径,并且已在许多领域显示出其优于单个分类器的良好性能,为此,提出基于集成学习理论的文本情感分类方法。实验结果显示三种常用的集成学习方法 Bagging、Boosting和Random Subspace对基础分类器的分类精度都有提高,并且在不同的基础分类器条件下,Random Subspace方法较Bagging和Boosting方法在统计意义上更优,以上结果进一步验证了集成学习理论在文本情感分类中应用的有效性。     

基于形态学属性剖面的高光谱影像集成分类

传统高光谱遥感影像逐像素分类方法未考虑像元之间的空间关联性且泛化性能较低。形态学属性剖面是表征影像空间结构的有效方法,同时集成学习可显著提升分类算法的泛化能力。为了在高光谱影像分类中充分利用影像的空间信息并提高分类的稳定性,提出一种基于形态学属性剖面高光谱遥感影像集成学习分类方法。首先,用主成分分析和最小噪声变换进行特征提取,并借助形态学属性剖面获取影像的多重空间特征;然后用极限学习和支持向量机的方法进行分类;最后将多个分类结果以多数投票的方式集成。区别于已有集成学习方法,综合考虑了不同特征提取和不同分类方法的联合集成,并将形态学属性剖面引入其中以充分利用影像的空间信息。采用AVIRIS和ROSIS两组高光谱数据检验该方法的分类性能,实验结果表明该方法可获得高精度和高稳定性的分类结果,总体精度分别达到83.41%和95.14%。     

Dynamic weighting ensemble classifiers based on cross-validation

Ensemble of classifiers constitutes one of the main current directions in machine learning and data mining. It is accepted that the ensemble methods can be divided into static and dynamic ones. Dynamic ensemble methods explore the use of different classifiers for different samples and therefore may get better generalization ability than static ensemble methods. However, for most of dynamic approaches based on KNN rule, additional part of training samples should be taken out for estimating “local classification performance” of each base classifier. When the number of training samples is not sufficient enough, it would lead to the lower accuracy of the training model and the unreliableness for estimating local performances of base classifiers, so further hurt the integrated performance. This paper presents a new dynamic ensemble model that introduces cross-validation technique in the process of local performances’ evaluation and then dynamically assigns a weight to each component classifier. Experimental results with 10 UCI data sets demonstrate that when the size of training set is not large enough, the proposed method can achieve better performances compared with some dynamic ensemble methods as well as some classical static ensemble approaches.     

Dynamically building diversified classifier pruning ensembles via canonical correlation analysis

Empirical studies on ensemble learning that combines multiple classifiers have shown that, it is an effective technique to improve accuracy and stability of a single classifier. In this paper, we propose a novel method of dynamically building diversified sparse ensembles. We first apply a technique known as the canonical correlation to model the relationship between the input data variables and output base classifiers. The canonical (projected) output classifiers and input training data variables are encoded globally through a multi-linear projection of CCA, to decrease the impacts of noisy input data and incorrect classifiers to a minimum degree in such a global view. Secondly, based on the projection, a sparse regression method is used to prune representative classifiers by combining classifier diversity measurement. Based on the above methods, we evaluate the proposed approach by several datasets, such as UCI and handwritten digit recognition. Experimental results of the study show that, the proposed approach achieves better accuracy as compared to other ensemble methods such as QFWEC, Simple Vote Rule, Random Forest, Drep and Adaboost.

     

改进的毫米波复数网络稀疏成像算法

针对基于压缩感知的重构方法耗时巨大的问题,从信号恢复的角度提出了一种基于深度学习方法的稀疏成像方案。首先,构建基于复数卷积的U-Net网络。其次,将欠采样信号输入网络得到满采样信号。最后,使用距离维脉压的二维匹配滤波算法重构出目标。实验建立在不同稀疏度和不同采样间隔下的欠采样仿真数据集中,并与传统和最近的信号处理方法进行对比。再使用实测数据进行验证,实验结果表明该算法在重构耗时以及图像平均梯度上具有更好的表现。     

An AK-BRP dictionary learning algorithm for video frame sparse representation in compressed sensing

Sparsifying transform is an important prerequisite in compressed sensing. And it is practically significant to research the fast and efficient signal sparse representation methods. In this paper, we propose an adaptive K-BRP (AK-BRP) dictionary learning algorithm. The bilateral random projection (BRP), a method of low rank approximation, is used to update the dictionary atoms. Furthermore, in the sparse coding stage, an adaptive sparsity constraint is utilized to obtain sparse representation coefficient and helps to improve the efficiency of the dictionary update stage further. Finally, for video frame sparse representation, our adaptive dictionary learning algorithm achieves better performance than K-SVD dictionary learning algorithm in terms of computation cost. And our method produces smaller reconstruction error as well.

     

Ensemble based on GA wrapper feature selection

Ensemble of classifiers is a learning paradigm where many classifiers are jointly used to solve a problem. Research has shown that ensemble is very effective for classification tasks. Diversity and accuracy are two basic requirements for the ensemble creation. In this paper, we propose an ensemble creation method based on GA wrapper feature selection. Preliminary experimental results on real-world data show that the proposed method is promising, especially when the number of training data is limited.