Online voltage prediction using gaussian process regression for fault-tolerant photovoltaic standalone applications

Neural Computing and Applications - This paper presents a fault detection system for photovoltaic standalone applications based on Gaussian Process Regression (GPR). The installation is a...     

Online reduced gaussian process regression based generalized likelihood ratio test for fault detection

In this paper we consider a new fault detection approach that merges the benefits of Gaussian process regression (GPR) with a generalized likelihood ratio test (GLRT). The GPR is one of the most well-known machine learning techniques. It is simpler and generally more robust than other methods. To deal with both high computational costs for large data sets and time-varying dynamics of industrial processes, we consider a reduced and online version of the GPR method. The online reduced GPR (ORGPR) aims to select a reduced set of kernel functions to build the GPR model and apply it for online fault detection based on GLRT chart. Compared with the conventional GPR technique, the proposed ORGPR method has the advantages of improving the computational efficiency by decreasing the dimension of the kernel matrix. The developed ORGPR-based GLRT (ORGPR-based GLRT) could improve the fault detection efficiency since it is able to track the time-varying characteristics of the processes. The fault detection performance of the developed ORGPR-based GLRT method is evaluated using a Tennessee Eastman process. The simulation results show that the proposed method outperforms the conventional GPR-based GLRT technique.     

基于高斯过程回归和信息分析法的常压塔操作优化

针对常压塔操作优化问题,通过高斯过程回归建立常压塔的元模型,并用信息分析法进行迭代计算,最终获取常压塔的最优操作条件。用2个实验验证了该算法的有效性:(1)固定常压塔三侧线产品的全塔效益最大化;(2)全塔综合效益最大化。从结果中可以看到,采用高斯过程回归建立常压塔模型进行优化,能够提高常压塔的经济效益。     

Augmented Lagrangian alternating direction method for matrix separation based on low-rank factorization

The matrix separation problem aims to separate a low-rank matrix and a sparse matrix from their sum. This problem has recently attracted considerable research attention due to its wide range of potential applications. Nuclear-norm minimization models have been proposed for matrix separation and proved to yield exact separations under suitable conditions. These models, however, typically require the calculation of a full or partial singular value decomposition at every iteration that can become increasingly costly as matrix dimensions and rank grow. To improve scalability, in this paper, we propose and investigate an alternative approach based on solving a non-convex, low-rank factorization model by an augmented Lagrangian alternating direction method. Numerical studies indicate that the effectiveness of the proposed model is limited to problems where the sparse matrix does not dominate the low-rank one in magnitude, though this limitation can be alleviated by certain data pre-processing techniques. On the other hand, extensive numerical results show that, within its applicability range, the proposed method in general has a much faster solution speed than nuclear-norm minimization algorithms and often provides better recoverability.     

基于超图表示的低秩属性选择方法用于回归分析*

针对现有的回归模型未考虑特征之间的深层结构,而导致在回归问题上输出不稳定的模型,提出了一种新的属性选择方法。具体地,通过稀疏学习理论中的 L2,1-范数和 L2,p-范数在线性回归模型分别进行样本降噪和属性选择,然后,利用超图结构和低秩约束来分别考虑数据间的局部结构和不同数据间的全局结构,最后结合子空间学习方法来对模型进行微调。经实验证明,在回归分析中该算法较对比算法能取得更好的效果。     

基于低秩重构表示的动态回归迁移模型

针对实际流程工业过程存在动态时变和概念漂移特性,导致软测量模型预测精度下降的问题,提出基于低秩重构表示的动态迁移回归模型.为了更好地描述动态过程,在动态内模型偏最小二乘框架下,将高维过程数据映射到低维潜变量空间中,以捕获质量变量与潜变量之间的动态相关性.为了减小概念漂移,在获得动态相关性的同时,通过增强不同工况质量变量估计值之间的相关性实现数据的条件分布对齐.在3个公开工业数据集上的实验结果表明:所提出模型的预测精度与静态基模型和动态基模型相比均有所提升,可以有效地提高模型的预测精度和泛化能力.     

Predictive performance of Dirichlet process shrinkage methods in linear regression

An obvious Bayesian nonparametric generalization of ridge regression assumes that coefficients are exchangeable, from a prior distribution of unknown form, which is given a Dirichlet process prior with a normal base measure. The purpose of this paper is to explore predictive performance of this generalization, which does not seem to have received any detailed attention, despite related applications of the Dirichlet process for shrinkage estimation in multivariate normal means, analysis of randomized block experiments and nonparametric extensions of random effects models in longitudinal data analysis. We consider issues of prior specification and computation, as well as applications in penalized spline smoothing. With a normal base measure in the Dirichlet process and letting the precision parameter approach infinity the procedure is equivalent to ridge regression, whereas for finite values of the precision parameter the discreteness of the Dirichlet process means that some predictors can be estimated as having the same coefficient. Estimating the precision parameter from the data gives a flexible method for shrinkage estimation of mean parameters which can work well when ridge regression does, but also adapts well to sparse situations. We compare our approach with ridge regression, the lasso and the recently proposed elastic net in simulation studies and also consider applications to penalized spline smoothing.     

Constrained linear quadratic gaussian control with process applications

Constrained linear quadratic Gaussian control is considered. Important practical design constraints including restrictions in control signal variations and in regulator structure are introduced quantitatively into the control problem formulation. Various topics in the resulting extension of the standard LQG design procedure are discussed, for instance optimality conditions, design of optimal low-order controllers and variance-constrained self-tuning control. Numerical algorithms for solving the constrained LQG control problems are given facilitating the application of the design procedure. Three industrial applications of linear quadratic Gaussian design are described. The examples are taken from the cement industry and from a process for the production of plastic film.     

Tree-based methods for online multi-target regression

Methods that address the task of multi-target regression on data streams are relatively weakly represented in the current literature. We present several different approaches to learning trees and ensembles of trees for multi-target regression based on the Hoeffding bound. First, we introduce a local method, which learns multiple single-target trees to produce multiple predictions, which are then aggregated into a multi-target prediction. We follow with a tree-based method (iSOUP-Tree) which learns trees that predict all of the targets at once. We then introduce iSOUP-OptionTree, which extends iSOUP-Tree through the use of option nodes. We continue with ensemble methods, and describe the use of iSOUP-Tree as a base learner in the online bagging and online random forest ensemble approaches. We describe an evaluation scenario, and present and discuss the results of the described methods, most notably in terms of predictive performance and the use of computational resources. Finally, we present two case studies where we evaluate the introduced methods in terms of their efficiency and viability of application to real world domains.     

Generation of gaussian pseudo-random process with specific correlation properties

A new method for the generation of a correlated pseudo-random gaussian process with a desired power spectral density or auto-correlation function is presented. Samples of the pseudo-random process are generated at the output of the cascade connection of a pseudo-random number (PN) generator and correlation-shaping finite impulse response filter. The proposed method generates a pseudo-random gaussian process, having arbitrary correlation properties, with a high degree of accuracy. Computer simulation examples are given to demonstrate the performance of the method.     

Fault prognosis of filamentous sludge bulking using an enhanced multi-output gaussian processes regression

The activated sludge process (ASP) is widely adopted to remove pollutants in wastewater treatment plants (WWTPs). However, the occurrence of filamentous sludge bulking often compromises the stable operation of the ASP. For timely diagnosis of filamentous sludge bulking for an activated sludge process in advance, this study proposed a Multi-Output Gaussian Processes Regression (MGPR) model for multi-step prediction and presented the Vector auto-regression (VAR) to learn the MGPR modelling deviation. The resulting models and associated uncertainty levels are used to monitor the filamentous sludge bulking related parameter, sludge volume index (SVI), such that the evolution of SVI can be predicted for both one-step and multi-step ahead. This methodology was validated with SVI data collected from one full-scale WWTP. Online diagnosis and prognosis of filamentous bulking sludge with real-time SVI prediction were tested through a simulation study. The results demonstrated that the proposed methodology was capable of predicting future SVI with good accuracy, thereby providing sufficient time for filamentous sludge bulking.     

Novel ensemble methods for regression via classification problems

Regression via classification (RvC) is a method in which a regression problem is converted into a classification problem. A discretization process is used to covert continuous target value to classes. The discretized data can be used with classifiers as a classification problem. In this paper, we use a discretization method, Extreme Randomized Discretization (ERD), in which bin boundaries are created randomly to create ensembles. We present two ensemble methods for RvC problems. We show theoretically that the proposed ensembles for RvC perform better than RvC with the equal-width discretization method. We also show the superiority of the proposed ensemble methods experimentally. Experimental results suggest that the proposed ensembles perform competitively to the method developed specifically for regression problems.     

Reduction-based methods and metrics for selective regression testing

In corrective maintenance, modified software is regression tested using selected test cases in order to ensure that the modifications have not caused adverse effects. This activity of selective regression testing involves regression test selection, which refers to selecting test cases from the previously run test suite, and test-coverage identification. In this paper, we propose three test-selection methods and two coverage identification metrics. The three methods aim to reduce the number of selected test cases for retesting the modified software. The first method, referred to as modification-based reduction version 1 (MBR1), selects a reduced number of test cases based on the modification made and its effects in the software. The second method, referred to as modification-based reduction version 2 (MBR2) improves MBR1 by further omitting tests that do not cover the modification. The third method, referred to as precise reduction (PR), reduces the number of test cases selected by omitting non-modification-revealing tests from the initial test suite. The two coverage metrics are McCabe-based regression test metrics, which are referred to as the Reachability regression Test selection McCabe-based metric (RTM), and data-flow Slices regression Test McCabe-based metric (STM). These metrics aim to assist the regression tester in monitoring test-coverage adequacy, reveal any shortage or redundancy in the test suite, and assist in identifying, where additional tests may be required for regression testing.We empirically compare MBR1, MBR2, and PR with three reduction and precision-oriented methods on 60 test-problems. The results show that PR selects the least number of test cases most of the time and omits non-modification-revealing tests. We also demonstrate the applicability of our proposed methods to object-oriented regression testing at the class level. Further, we illustrate typical application of the RTM and STM metrics using the 60 test-problems and two coverage-oriented selective regression-testing methods.     

结合高斯过程和形变模型的超声图像分割方法

目标区域的先验形状在基于形变模型的超声图像分割方法中扮演着重要的角色。为了提高先验形状模型对目标轮廓形变细节的建模能力,提出了一种基于高斯过程的统计形状模型。目标的形状被表示成一种离散的随机时间序列;利用高斯过程的性质对训练集中的目标形状变化进行统计学习,从而生成目标的先验形状和先验概率。为给形变模型向目标区域的演化提供观测模型,结合超声图像中目标边缘内外灰度变化特征设计了一种径向纹理特征模型。分割的优化被转化为求最大后验概率的过程。基于真实的临床超声图像实验结果显示,与其他方法相比该方法在复杂形变区域和弱边缘区域提供了更准确和鲁棒的结果。     

高斯过程回归方法综述

高斯过程回归是基于贝叶斯理论和统计学习理论发展起来的一种全新机器学习方法,适于处理高维数、小样本和非线性等复杂回归问题。在阐述该方法原理的基础上,分析了其存在的计算量大、噪声必须服从高斯分布等问题,给出了改进方法。与神经网络和支持向量机相比,该方法具有容易实现、超参数自适应获取以及输出具有概率意义等优点,方便与预测控制、自适应控制、贝叶斯滤波等相结合。最后总结了其应用情况并展望了未来发展方向。     

Quantile regression methods with varying-coefficient models for censored data

Considerable intellectual progress has been made to the development of various semiparametric varying-coefficient models over the past ten to fifteen years. An important advantage of these models is that they avoid much of the curse of dimensionality problem as the nonparametric functions are restricted only to some variables. More recently, varying-coefficient methods have been applied to quantile regression modeling, but all previous studies assume that the data are fully observed. The main purpose of this paper is to develop a varying-coefficient approach to the estimation of regression quantiles under random data censoring. We use a weighted inverse probability approach to account for censoring, and propose a majorize–minimize type algorithm to optimize the non-smooth objective function. The asymptotic properties of the proposed estimator of the nonparametric functions are studied, and a resampling method is developed for obtaining the estimator of the sampling variance. An important aspect of our method is that it allows the censoring time to depend on the covariates. Additionally, we show that this varying-coefficient procedure can be further improved when implemented within a composite quantile regression framework. Composite quantile regression has recently gained considerable attention due to its ability to combine information across different quantile functions. We assess the finite sample properties of the proposed procedures in simulated studies. A real data application is also considered.     

Robust regression methods for computer vision: A review

Regression analysis (fitting a model to noisy data) is a basic technique in computer vision, Robust regression methods that remain reliable in the presence of various types of noise are therefore of considerable importance. We review several robust estimation techniques and describe in detail the least-median-of-squares (LMedS) method. The method yields the correct result even when half of the data is severely corrupted. Its efficiency in the presence of Gaussian noise can be improved by complementing it with a weighted least-squares-based procedure. The high time-complexity of the LMedS algorithm can be reduced by a Monte Carlo type speed-up technique. We discuss the relationship of LMedS with the RANSAC paradigm and its limitations in the presence of noise corrupting all the data, and we compare its performance with the class of robust M-estimators. References to published applications of robust techniques in computer vision are also given.