Kernel Principal Component Analysis (KPCA)

MATLAB code for dimensionality reduction, fault detection, and fault diagnosis using KPCA

Version 2.2, 14-MAY-2021

Email: iqiukp@outlook.com

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Main features

• Easy-used API for training and testing KPCA model
• Support for dimensionality reduction, data reconstruction, fault detection, and fault diagnosis
• Multiple kinds of kernel functions (linear, gaussian, polynomial, sigmoid, laplacian)
• Visualization of training and test results
• Component number determination based on given explained level or given number

Notices

• Only fault diagnosis of Gaussian kernel is supported.
• This code is for reference only.

How to use

01. Kernel funcions

A class named Kernel is defined to compute kernel function matrix.

%{
        type   -
        
        linear      :  k(x,y) = x'*y
        polynomial  :  k(x,y) = (γ*x'*y+c)^d
        gaussian    :  k(x,y) = exp(-γ*||x-y||^2)
        sigmoid     :  k(x,y) = tanh(γ*x'*y+c)
        laplacian   :  k(x,y) = exp(-γ*||x-y||)
    
    
        degree -  d
        offset -  c
        gamma  -  γ
%}
kernel = Kernel('type', 'gaussian', 'gamma', value);
kernel = Kernel('type', 'polynomial', 'degree', value);
kernel = Kernel('type', 'linear');
kernel = Kernel('type', 'sigmoid', 'gamma', value);
kernel = Kernel('type', 'laplacian', 'gamma', value);

For example, compute the kernel matrix between X and Y

X = rand(5, 2);
Y = rand(3, 2);
kernel = Kernel('type', 'gaussian', 'gamma', 2);
kernelMatrix = kernel.computeMatrix(X, Y);
>> kernelMatrix

kernelMatrix =

    0.5684    0.5607    0.4007
    0.4651    0.8383    0.5091
    0.8392    0.7116    0.9834
    0.4731    0.8816    0.8052
    0.5034    0.9807    0.7274

02. Simple KPCA model for dimensionality reduction

clc
clear all
close all
addpath(genpath(pwd))

load('.\data\helix.mat', 'data')
kernel = Kernel('type', 'gaussian', 'gamma', 2);
parameter = struct('numComponents', 2, ...
                   'kernelFunc', kernel);
% build a KPCA object
kpca = KernelPCA(parameter);
% train KPCA model
kpca.train(data);

%　mapping data
mappingData = kpca.score;

% Visualization
kplot = KernelPCAVisualization();
% visulize the mapping data
kplot.score(kpca)

The training results (dimensionality reduction):

*** KPCA model training finished ***
running time            = 0.2798 seconds
kernel function         = gaussian 
number of samples       = 1000 
number of features      = 3 
number of components    = 2 
number of T2 alarm      = 135 
number of SPE alarm     = 0 
accuracy of T2          = 86.5000% 
accuracy of SPE         = 100.0000% 

Another application using banana-shaped data:

03. Simple KPCA model for reconstruction

clc
clear all
close all
addpath(genpath(pwd))

load('.\data\circle.mat', 'data')
kernel = Kernel('type', 'gaussian', 'gamma', 0.2);
parameter = struct('numComponents', 2, ...
                   'kernelFunc', kernel);
% build a KPCA object
kpca = KernelPCA(parameter);
% train KPCA model
kpca.train(data);

%　reconstructed data
reconstructedData = kpca.newData;

% Visualization
kplot = KernelPCAVisualization();
kplot.reconstruction(kpca)

04. Component number determination

The Component number can be determined based on given explained level or given number.

Case 1

The number of components is determined by the given explained level. The given explained level should be 0 < explained level < 1. For example, when explained level is set to 0.75, the parameter should be set as:

parameter = struct('numComponents', 0.75, ...
                   'kernelFunc', kernel);

The code is

clc
clear all
close all
addpath(genpath(pwd))

load('.\data\TE.mat', 'trainData')
kernel = Kernel('type', 'gaussian', 'gamma', 1/128^2);

parameter = struct('numComponents', 0.75, ...
                   'kernelFunc', kernel);
% build a KPCA object
kpca = KernelPCA(parameter);
% train KPCA model
kpca.train(trainData);

% Visualization
kplot = KernelPCAVisualization();
kplot.cumContribution(kpca)

As shown in the image, when the number of components is 21, the cumulative contribution rate is 75.2656%，which exceeds the given explained level (0.75）.

Case 2

The number of components is determined by the given number. For example, when the given number is set to 24, the parameter should be set as:

parameter = struct('numComponents', 24, ...
                   'kernelFunc', kernel);

The code is

clc
clear all
close all
addpath(genpath(pwd))

load('.\data\TE.mat', 'trainData')
kernel = Kernel('type', 'gaussian', 'gamma', 1/128^2);

parameter = struct('numComponents', 24, ...
                   'kernelFunc', kernel);
% build a KPCA object
kpca = KernelPCA(parameter);
% train KPCA model
kpca.train(trainData);

% Visualization
kplot = KernelPCAVisualization();
kplot.cumContribution(kpca)

As shown in the image, when the number of components is 24, the cumulative contribution rate is 80.2539%.

05. Fault detection

Demonstration of fault detection using KPCA (TE process data)

clc
clear all
close all
addpath(genpath(pwd))

load('.\data\TE.mat', 'trainData', 'testData')
kernel = Kernel('type', 'gaussian', 'gamma', 1/128^2);
parameter = struct('numComponents', 0.65, ...
                   'kernelFunc', kernel);
               
% build a KPCA object
kpca = KernelPCA(parameter);
% train KPCA model
kpca.train(trainData);
% test KPCA model
results = kpca.test(testData);

% Visualization
kplot = KernelPCAVisualization();
kplot.cumContribution(kpca)
kplot.trainResults(kpca)
kplot.testResults(kpca, results)

The training results are

*** KPCA model training finished ***
running time            = 0.0986 seconds
kernel function         = gaussian 
number of samples       = 500 
number of features      = 52 
number of components    = 16 
number of T2 alarm      = 16 
number of SPE alarm     = 17 
accuracy of T2          = 96.8000% 
accuracy of SPE         = 96.6000% 

The test results are

*** KPCA model test finished ***
running time            = 0.0312 seconds
number of test data     = 960 
number of T2 alarm      = 799 
number of SPE alarm     = 851 

06. Fault diagnosis

Notice

• If you want to calculate CPS of a certain time, you should set starting time equal to ending time. For example, 'diagnosis', [500, 500]
• If you want to calculate the average CPS of a period of time, starting time and ending time should be set respectively. 'diagnosis', [300, 500]
• The fault diagnosis module is only supported for gaussian kernel function and it may still take a long time when the number of the training data is large.

clc
clear all
close all
addpath(genpath(pwd))

load('.\data\TE.mat', 'trainData', 'testData')
kernel = Kernel('type', 'gaussian', 'gamma', 1/128^2);

parameter = struct('numComponents', 0.65, ...
                   'kernelFunc', kernel,...
                   'diagnosis', [300, 500]);
               
% build a KPCA object
kpca = KernelPCA(parameter);
% train KPCA model
kpca.train(trainData);
% test KPCA model
results = kpca.test(testData);

% Visualization
kplot = KernelPCAVisualization();
kplot.cumContribution(kpca)
kplot.trainResults(kpca)
kplot.testResults(kpca, results)
kplot.diagnosis(results)

Diagnosis results:

*** Fault diagnosis ***
Fault diagnosis start...
Fault diagnosis finished.
running time            = 18.2738 seconds
start point             = 300 
ending point            = 500 
fault variables (T2)    = 44   1   4 
fault variables (SPE)   = 1  44  18