一种基于标签传播的半监督核学习算法

一个好的核函数能提升机器学习模型的有效性,但核函数的选择并不容易,其与问题背景密切相关,且依赖于领域知识和经验。核学习是一种通过训练数据集寻找最优核函数的机器学习方法,能通过有监督学习的方式寻找到一组基核函数的最优加权组合。考虑到训练数据集获取标签的代价,提出一种基于标签传播的半监督核学习方法,该方法能够同时利用有标签数据和无标签数据进行核学习,通过半监督学习中被广泛使用的标签传播方法结合和谐函数获得数据集统一的标签分布。在UCI数据集上对提出的算法进行性能评估,结果表明该方法是有效的。     

流形极限学习机自编码特征表示

极限学习机（ELM）作为一种无监督分类方法,具有学习速度快、泛化性能高、逼近能力好的优点。随着无监督学习的发展,将ELM与自动编码器集成已成为无标签数据集提取特征的新视角,如极限学习机自动编码器（ELM-AE）是一种无监督的神经网络,无需迭代即可找到代表原始样本和其学习过程的主要成分。其重建输入信号获取原始样本的主要特征,且考虑了原始数据的全局信息以避免信息的丢失,然而这类方法未考虑数据的固有流形结构即样本间的近邻结构关系。借鉴极限学习机自动编码器的思想,提出了一种基于流形的极限学习机自动编码器算法（M-ELM）。该算法是一种非线性无监督特征提取方法,结合流形学习保持数据的局部信息,且在特征提取过程中同时对相似度矩阵进行学习。通过在IRIS数据集、脑电数据集和基因表达数据集上进行实验,将该算法与其他无监督学习方法PCA、LPP、NPE、LE和ELM-AE算法经过[k]-means聚类后的准确率进行了比较,以表明该算法的有效性。     

半监督局部判别分析

针对无监督学习及有监督学习算法的缺点,提出一种半监督局部判别分析的线性降维算法。数据在没有足够的训练样本时,局部结构比全局结构更重要。算法在每一个局部区域利用有标签数据推导出数据的局部判别结构,无标签数据和有标签数据推导出数据的内在几何结构。在ORL和Yale人脸数据库上的实验结果表明该算法是有效的。     

无模型强化学习研究综述

强化学习(Reinforcement Learning,RL)作为机器学习领域中与监督学习、无监督学习并列的第三种学习范式,通过与环境进行交互来学习,最终将累积收益最大化。常用的强化学习算法分为模型化强化学习(Model-based Reinforcement Lear-ning)和无模型强化学习(Model-free Reinforcement Learning)。模型化强化学习需要根据真实环境的状态转移数据来预定义环境动态模型,随后在通过环境动态模型进行策略学习的过程中无须再与环境进行交互。在无模型强化学习中,智能体通过与环境进行实时交互来学习最优策略,该方法在实际任务中具有更好的通用性,因此应用范围更广。文中对无模型强化学习的最新研究进展与发展动态进行了综述。首先介绍了强化学习、模型化强化学习和无模型强化学习的基础理论;然后基于价值函数和策略函数归纳总结了无模型强化学习的经典算法及各自的优缺点;最后概述了无模型强化学习在游戏AI、化学材料设计、自然语言处理和机器人控制领域的最新研究现状,并对无模型强化学习的未来发展趋势进行了展望。     

基于自编码神经网络的半监督联邦学习模型

联邦学习是一种新型的分布式机器学习方法,可以使得各客户端在不分享隐私数据的前提下共同建立共享模型。然而现有的联邦学习框架仅适用于监督学习,即默认所有客户端数据均带有标签。由于现实中标记数据难以获取,联邦学习模型训练的前提假设通常很难成立。为解决此问题,对原有联邦学习进行扩展,提出了一种基于自编码神经网络的半监督联邦学习模型ANN-SSFL,该模型允许无标记的客户端参与联邦学习。无标记数据利用自编码神经网络学习得到可被分类的潜在特征,从而在联邦学习中提供无标记数据的特征信息来作出自身贡献。在MNIST数据集上进行实验,实验结果表明,提出的ANN-SSFL模型实际可行,在监督客户端数量不变的情况下,增加无监督客户端可以提高原有联邦学习精度。     

一种基因数据分析的半监督学习算法

基于对无标记数据算法的研究,讨论了基因数据分析的半监督学习算法。基因数据的典型特征是小样本、高維数,处理起来非常困难。在安全的半监督学习基础上,提出了一种降维和半监督学习相结合的方法,以提高分类效果的精确度及鲁棒性。实验证明,该方法通过结合降维和半监督学习的优点,具有很好的应用价值。     

主动协同半监督粗糙集分类模型

粗糙集理论是一种有监督学习模型,一般需要适量有标记的数据来训练分类器。但现实一些问题往往存在大量无标记的数据,而有标记数据由于标记代价过大较为稀少。文中结合主动学习和协同训练理论,提出一种可有效利用无标记数据提升分类性能的半监督粗糙集模型。该模型利用半监督属性约简算法提取两个差异性较大的约简构造基分类器,然后基于主动学习思想在无标记数据中选择两分类器分歧较大的样本进行人工标注,并将更新后的分类器交互协同学习。UCI数据集实验对比分析表明,该模型能明显提高分类学习性能,甚至能达到数据集的最优值。     

面向心脏MRI分割的半监督空间一致性约束网络

精准分割心脏磁共振图像(MRI)分割对于心脏功能分析至关重要.当前基于数据驱动的神经网络模型极大地促进了心脏MRI分割的发展,然而对标注数据的依赖极大地限制了神经网络模型在心脏MRI分割领域的应用.为了降低神经网络模型对于标注数据的依赖,提出一种基于无监督空间一致性约束的半监督心脏MRI分割方法,在少量有标注数据的监督学习基础上,利用无标签数据在模型输入端和输出端分别进行空间变换后前后一致的特性,构建对于无标注数据的空间一致性约束.使用ACDC 2017心脏多组织分割数据集评估了所提出的方法,实验结果表明,相对于有监督学习,通过无监督数据的空间一致性约束能够显著提升模型的泛化能力;此外,相对于其他state-of-the-art的半监督方法,文中方法也拥有更优的泛化性能.     

一种鲁棒的半监督联邦学习系统

联邦学习允许边缘设备或客户端将数据存储在本地来合作训练共享的全局模型。主流联邦学习系统通常基于客户端本地数据有标签这一假设,然而客户端数据一般没有真实标签,且数据可用性和数据异构性是联邦学习系统面临的主要挑战。针对客户端本地数据无标签的场景,设计一种鲁棒的半监督联邦学习系统。利用FedMix方法分析全局模型迭代之间的隐式关系,将在标签数据和无标签数据上学习到的监督模型和无监督模型进行分离学习。采用FedLoss聚合方法缓解客户端之间数据的非独立同分布（non-IID）对全局模型收敛速度和稳定性的影响,根据客户端模型损失函数值动态调整局部模型在全局模型中所占的权重。在CIFAR-10数据集上的实验结果表明,该系统的分类准确率相比于主流联邦学习系统约提升了3个百分点,并且对不同non-IID水平的客户端数据更具鲁棒性。     

基于多示例的K-means聚类学习算法

多示例学习是继监督学习、非监督学习、强化学习后的又一机器学习框架。将多示例学习和非监督学习结合起来,在传统非监督聚类算法K-means的基础上提出MIK-means算法,该算法利用混合Hausdorff距离作为相似测度来实现数据聚类。实验表明,该方法能够有效揭示多示例数据集的内在结构,与K-means算法相比具有更好的聚类效果。     

A reinforcement learning approach to online clustering

A general technique is proposed for embedding online clustering algorithms based on competitive learning in a reinforcement learning framework. The basic idea is that the clustering system can be viewed as a reinforcement learning system that learns through reinforcements to follow the clustering strategy we wish to implement. In this sense, the reinforcement guided competitive learning (RGCL) algorithm is proposed that constitutes a reinforcement-based adaptation of learning vector quantization (LVQ) with enhanced clustering capabilities. In addition, we suggest extensions of RGCL and LVQ that are characterized by the property of sustained exploration and significantly improve the performance of those algorithms, as indicated by experimental tests on well-known data sets.     

Generalized clustering networks and Kohonen''s self-organizingscheme

The relationship between the sequential hard c-means (SHCM) and learning vector quantization (LVQ) clustering algorithms is discussed. The impact and interaction of these two families of methods with Kohonen's self-organizing feature mapping (SOFM), which is not a clustering method but often lends ideas to clustering algorithms, are considered. A generalization of LVQ that updates all nodes for a given input vector is proposed. The network attempts to find a minimum of a well-defined objective function. The learning rules depend on the degree of distance match to the winner node; the lesser the degree of match with the winner, the greater the impact on nonwinner nodes. Numerical results indicate that the terminal prototypes generated by this modification of LVQ are generally insensitive to initialization and independent of any choice of learning coefficient. IRIS data obtained by E. Anderson's (1939) is used to illustrate the proposed method. Results are compared with the standard LVQ approach.     

Soft learning vector quantization and clustering algorithms basedon ordered weighted aggregation operators

This paper presents the development and investigates the properties of ordered weighted learning vector quantization (LVQ) and clustering algorithms. These algorithms are developed by using gradient descent to minimize reformulation functions based on aggregation operators. An axiomatic approach provides conditions for selecting aggregation operators that lead to admissible reformulation functions. Minimization of admissible reformulation functions based on ordered weighted aggregation operators produces a family of soft LVQ and clustering algorithms, which includes fuzzy LVQ and clustering algorithms as special cases. The proposed LVQ and clustering algorithms are used to perform segmentation of magnetic resonance (MR) images of the brain. The diagnostic value of the segmented MR images provides the basis for evaluating a variety of ordered weighted LVQ and clustering algorithms.     

An axiomatic approach to soft learning vector quantization andclustering

This paper presents an axiomatic approach to soft learning vector quantization (LVQ) and clustering based on reformulation. The reformulation of the fuzzy c-means (FCM) algorithm provides the basis for reformulating entropy-constrained fuzzy clustering (ECFC) algorithms. According to the proposed approach, the development of specific algorithms reduces to the selection of a generator function. Linear generator functions lead to the FCM and fuzzy learning vector quantization algorithms while exponential generator functions lead to ECFC and entropy-constrained learning vector quantization algorithms. The reformulation of LVQ and clustering algorithms also provides the basis for developing uncertainty measures that can identify feature vectors equidistant from all prototypes. These measures are employed by a procedure developed to make soft LVQ and clustering algorithms capable of identifying outliers in the data set. This procedure is evaluated by testing the algorithms generated by linear and exponential generator functions on speech data.     

学习矢量量化的推广及其典型形式的比较

无监督学习矢量量化(LVQ)是一类基于最小化风险函数的聚类方法,文中通过对无监督LVQ风险函数的研究,提出了无监督LVQ算法的广义形式,在此基础上将当前典型的LVQ算法表示为基于不同尺度函数的LVQ算法,极大地方便了学习矢量量化神经网络的推广与应用。通过对无监督LVQ神经网络的改造,得到了基于无监督聚类算法的有监督LVQ神经网络,并将其应用于说话人辨认,取得了满意的结果并比较了几种典型聚类算法的优劣。     

Soft learning vector quantization and clustering algorithms based on non-Euclidean norms: multinorm algorithms

This paper presents the development of soft clustering and learning vector quantization (LVQ) algorithms that rely on multiple weighted norms to measure the distance between the feature vectors and their prototypes. Clustering and LVQ are formulated in this paper as the minimization of a reformulation function that employs distinct weighted norms to measure the distance between each of the prototypes and the feature vectors under a set of equality constraints imposed on the weight matrices. Fuzzy LVQ and clustering algorithms are obtained as special cases of the proposed formulation. The resulting clustering algorithm is evaluated and benchmarked on three data sets that differ in terms of the data structure and the dimensionality of the feature vectors. This experimental evaluation indicates that the proposed multinorm algorithm outperforms algorithms employing the Euclidean norm as well as existing clustering algorithms employing weighted norms.     

Soft learning vector quantization and clustering algorithms based on non-Euclidean norms: single-norm algorithms

This paper presents the development of soft clustering and learning vector quantization (LVQ) algorithms that rely on a weighted norm to measure the distance between the feature vectors and their prototypes. The development of LVQ and clustering algorithms is based on the minimization of a reformulation function under the constraint that the generalized mean of the norm weights be constant. According to the proposed formulation, the norm weights can be computed from the data in an iterative fashion together with the prototypes. An error analysis provides some guidelines for selecting the parameter involved in the definition of the generalized mean in terms of the feature variances. The algorithms produced from this formulation are easy to implement and they are almost as fast as clustering algorithms relying on the Euclidean norm. An experimental evaluation on four data sets indicates that the proposed algorithms outperform consistently clustering algorithms relying on the Euclidean norm and they are strong competitors to non-Euclidean algorithms which are computationally more demanding.     

Neural clustering networks based on global optimisation of prototypes in metric spaces

The utilisation of clustering algorithms based on the optimisation of prototypes in neural networks is demonstrated for unsupervised learning. Stimulated by common clustering methods of this type (learning vector quantisation [LVQ, GLVQ] and K-means) a globally operating algorithm was developed to cope with known shortcomings of existing tools. This algorithm and K-means (for the common methods) were applied to the problem of clustering EEG patterns being pre-processed. It can be shown that the algorithm based on global random optimisation may find an optimal solution repeatedly, whereas K-means provides different sub-optimal solutions with respect to the quality measure defined as objective function. The results are presented. The performance of the algorithms is discussed.     

连续状态自适应离散化基于K-均值聚类的强化学习方法

使用聚类算法对连续状态空间进行自适应离散化．得到了基于K-均值聚类的强化学习方法．该方法的学习过程分为两部分：对连续状态空间进行自适应离散化的状态空间学习，使用K-均值聚类算法；寻找最优策略的策略学习．使用替代合适迹Sarsa学习算法．对连续状态的强化学习基准问题进行仿真实验，结果表明该方法能实现对连续状态空间的自适应离散化，并最终学习到最优策略．与基于CMAC网络的强化学习方法进行比较．结果表明该方法具有节省存储空间和缩短计算时间的优点．     

遗传LVQ聚类算法

Kohonen提出了学习矢量量化(LVQ)聚类算法及网络对聚类分析产生了深刻的影响,但LVQ存在神经元未被充分利用以及算法对初值敏感的问题。通过对LVQ聚类算法进行分析,根据基因算法的特点,论文提出一种结合基因算法与LVQ聚类算法的改进方法。实验结果证明改进的算法较LVQ聚类算法对初值具有明显的稳定性和有效性。