Machine Learning Using Support Vector Machines (Paper Review) Presented to: Prof. Dr. Mohamed...

Machine Learning Using Support Vector Machines

(Paper Review)

Presented to: Prof. Dr. Mohamed Batouche

Prepared By: Asma B. Al-Saleh Amani A. Al-Ajlan

427220094 427220111

King Saud UniversityThe College of Computer & Information Science

Computer Science Department (Master)Neural Networks and Machine Learning Applications (CSC 563 )

Spring 2008

Paper Information Title: Machine Learning Using Support Vector

Machines.

Authors: Abdul Rahim Ahmad. Marzuki Khalid. Rubiyah Yusof.

Publisher: MSTC 2002, Johor Bahru.

Date: September 2002.

Review Outlines

Introduction Artificial Neural Network (ANN) Support Vector Machine (SVM)

Support Vectors Theory of SVM Quadratic Programming Non-linear SVM SVM Implementations SVM for Multi-class Classification

Handwriting Recognition Experimental Results ANN vs. SVM Conclusion

Introduction

Introduction

The aim of this paper is to Present SVM as a comparison to ANN. Show the concept of SVM by providing

them some details about SVM.

Machine Learning

Machine Learning (ML) Constructing computer program that

automatically improve its performance with experience.

???Learned

Data

Machine Learning (ML) Applications

1. Data mining programs.2. Information filtering systems.3. Autonomous vehicles.4. Pattern recognition system:

Speech recognition. Handwriting recognition. Face recognition. Text categorization.

Artificial NeuralNetwork

Artificial Neural Network (ANN)

Massively parallel computing systems consisting of an extremely large number of simple processors with many interconnections.

Artificial Neural Network (ANN)

The main characteristics of ANN are:1. Ability to learn complex nonlinear input-

output relationships2. They use sequential training procedures to

updating (adapt) network architecture and connection weights so that a network can work efficiently.

Artificial Neural Network (ANN) In the area of pattern classification,

the feed-forward network is most popularly used.

Pattern Classification

Data Clustering

Multilayer perceptron (MLP) Radial-BasisFunction (RBF) networks

Kohonen Self-Organizing Map (SOM)

ANN and Pattern Recognition

ANN is low dependence on domain-specific knowledge compared to rule-based approaches.

Availability of efficient learning algorithms to use.

Support VectorMachine

Support Vector Machine – (SVM) SVM was introduced in 1992 by

Vapnik and his coworkers. SVM original form:

Binary classifier; separates between two classes.

Design for linear and separable data set. SVM used for classification and

regression.

Support Vector Machine – (SVM)

Theory of SVM

H1

H

H2W

Constraints

1. No data points between H1 and H2.

2. Margin between H1 and H2 is maximized.

-

H1

H

H2W

Support VectorsSolution: expressed as

a linear combination of support vectors:

• Subset of training patterns• Close to the decision boundary

Theory of SVM training data:{ , , ……, } Where:

),( 11 yx ),( 22 yx ),( nn yx

SVM

Class or label

Input features

di Rx }1,1{ iy

iy

Theory of SVM

H1

H

H2W

Class 1:

1. bxw

Class 2:

1. bxw

1).( bxwy ii

Theory of SVM

).sgn()( bxwxf

Learn a linear separating hyper plane classifier:

Quadratic Programming to maximize the margin , we need

to minimize:

Quadratic Programming solved by introducing Lagrange multipliers

||||

2

w2||||

2

1w

),,( bwL 2||||2

1w

N

i iii bwxy1

).(

N

i i1

Lagrange Multipliers

Maximize L where w and b are eliminated:

and

ji jijiji xxyy

,2

1

N

i i1DL

),,( bwL 2||||2

1w

N

i iii bwxy1

).(

N

i i1

Theory of SVM

Discriminate function:

)(xf ).sgn((1

bxxyN

i iii

Non-linear SVM

1. SVM mapped the data sets of input space into a higher dimensional feature space

2. Linear and the large-margin learning algorithm is then applied.

Non-linear SVM

Input (data) space(Non- linear)

)(xx

Feature space(Linear)

Non-linear SVM If the mapping function is ,we just

solve:

However, the mapping can be implicitly done by kernel functions:

)(.).(2

1, jji ijiji xxyy

N

i i1DL

ji jijiji xxkyy

,),(

2

1

N

i i1DL

Non-linear SVM

Discriminate function:

)(xf )),(sgn((1

bxxkyN

i iii

Kernel

There are many kernels that can be used that way.

Any kernel that satisfies Mercer’s condition can be used.

Kernel - Examples Polynomial kernels

Hyperbolic tangent

Radial basis function (Gaussian kernel)

Non-separable Input Space In real world problem, there is always

noise. Noise Non-separable data. Slack variables are introduced to each

input:

Penalty Parameter C: control overfitting.

iii bxwy 1).(

Non-separable Input Space

H1

H

H2

1

.

bxw

0

.

bxw

1

.

bxw

j

j

i

i

SVM for Multi-class Classification

Basic SVM is binary classifier; separates between two classes.

In real world, more than two classes is usually needed.

Ex: handwriting recognition

SVM for Multi-class Classification

Methods

Modifying binary to incorporate multi-class learning.

Combining binary

classifiers

One vs. One

K (K-1) /2

One vs. All

K

SVM for Multi-class Classification One vs. One and DAGSVM (Directed

Acyclic Graph) are the best choices for practical use.

they are: Less complex Easy to construct Faster to train.

Tapia et al, 2005

SVM Implementation Quadratic programming (QP) which is

computationally intensive.

However, many decomposition methods have been proposed that avoids the QP and makes SVM learning practical for many current problems.

Ex: Sequential Minimal Optimization (SMO)

Results of Experimental Studies

Data Handwritten digit database:

MNIST dataset.

USPS dataset. more difficult; human recognition error rate

is as high as 2.5%.

Error rate comparison of ANN, SVM and other algorithms for MNIST and USPS database.

1. SVM error rate is significantly lower than most other algorithms except for LeNet 5 NN.

2. Training time for SVM was significantly slower the higher recognition rate (low error rate) justify for the usage.

3. SVM usage should be increasing and replacing ANN in the area of handwriting recognition where faster method of implementing SVM have been introduced recently.

Results of Experimental Studies

SVM vs. ANNSVM ANN

Naturally handles multi-class classification.

Multi-class implementation needs to be performed.

ANN is known to overfit data unless cross-validation is applied.

SVM does not overfit data (Structural Risk Minimization).

Local minimum Global minimum.

Conclusion SVM is Powerful and is a useful alternative to

neural networks.

SVM find Global, unique solution.

Two key concepts of SVM: maximize the margin and choice of kernel.

Performance depends on choice of kernel and

parameters Still a research topic.

Training is memory-intensive due to QP.

Conclusion

Many active research is taking place on areas related to SVM.

Many SVM implementations are available on the Web:

SVMLight LIBSVM

Thank you…..

Questions?