Self organizing maps 1 iCSC2014, Juan López González, University of Oviedo Self organizing maps A visualization technique with data dimension reduction Juan López González University of Oviedo Inverted CERN School of Computing, February 2014

Self organizing maps 2 iCSC2014, Juan López González, University of Oviedo General overview  Lecture 1  Machine learning  Introduction  Definition  Problems  Techniques  Lecture 2  ANN introduction  SOM  Simulation  SOM based models

Self organizing maps 3 iCSC2014, Juan López González, University of Oviedo LECTURE 1 Self organizing maps. A visualization technique with data dimension reduction.

Self organizing maps 4 iCSC2014, Juan López González, University of Oviedo 1. Artificial neural networks (ANN)

Self organizing maps 5 iCSC2014, Juan López González, University of Oviedo 1.1. Introduction

Self organizing maps 6 iCSC2014, Juan López González, University of Oviedo Feedforward NN Recurrent NN Self organizing NN Others 1.2. Types

Self organizing maps 7 iCSC2014, Juan López González, University of Oviedo Feedforward NN

Self organizing maps 8 iCSC2014, Juan López González, University of Oviedo  Single layer feedforward Feedforward NN

Self organizing maps 9 iCSC2014, Juan López González, University of Oviedo  Multi-layer feedforward Feedforward NN  Supervised learning  Backpropagation learning algorithm

Self organizing maps 10 iCSC2014, Juan López González, University of Oviedo Recurrent neural networks

Self organizing maps 11 iCSC2014, Juan López González, University of Oviedo  Elman networks  ‘Context units’  Maintain state Recurrent neural networks

Self organizing maps 12 iCSC2014, Juan López González, University of Oviedo  Hopefield network  Symmetric connections  Associative memory Recurrent neural networks

Self organizing maps 13 iCSC2014, Juan López González, University of Oviedo  Modular neural networks  The human brain is not a massive network but a collection of small networks Recurrent neural networks

Self organizing maps 14 iCSC2014, Juan López González, University of Oviedo  Self-organizing networks  A set of neurons learn to map points in an input space to coordinates in an output space Self-organizing networks

Self organizing maps 15 iCSC2014, Juan López González, University of Oviedo  Holographic associative memory  Instantaneously trained networks  Learning vector quantization  Neuro-fuzzy networks  … Others

Self organizing maps 16 iCSC2014, Juan López González, University of Oviedo 2.1. Motivation 2.2. Goal 2.3. Main properties 2.4. Elements 2.5. Algorithm 2. Self-organizing maps

Self organizing maps 17 iCSC2014, Juan López González, University of Oviedo 2.1. Motivation  Topographic maps  Different sensory inputs (motor, visual, auditory…) are mapped in areas of the cerebral cortex in an orderly fashion

Self organizing maps 18 iCSC2014, Juan López González, University of Oviedo 2.1. Motivation  “The spatial location of an output neuron in a topographic map corresponds to a particular domain or feature drawn from the input space” Auditory cortical fields Motor-somatotopic maps

Self organizing maps 19 iCSC2014, Juan López González, University of Oviedo 2.2. Goal  Transform incoming signal of arbitrary dimension into a dimensional discrete map in a topologically ordered fashion

Self organizing maps 20 iCSC2014, Juan López González, University of Oviedo 2.3. Main properties  Transform continuos input space to discrete output space  Dimension reduction  winner-takes-all neuron  Ordered feature map Input with similar characteristics produce similar ouput

Self organizing maps 21 iCSC2014, Juan López González, University of Oviedo Dimension reduction  Curse of dimensionality (Richard E. Bellman)  The amount of data needed grows exponentially with the dimensionality  Types  Feature extraction  Reduce input data (features vector)  Feature selection  Select subset (remove redundant and irrelevant data)

Self organizing maps 22 iCSC2014, Juan López González, University of Oviedo 2.4. Elements  …of machine learning  A pattern exists  We don’t know how to solve it mathematically  A lot of data  (a 1,b 1,..,n 1 ), (a 2,b 2,..,n 2 ) … (a N,b N,..,n N )

Self organizing maps 23 iCSC2014, Juan López González, University of Oviedo 2.4. Elements  Lattice of neurons  Size?  Weights

Self organizing maps 24 iCSC2014, Juan López González, University of Oviedo 2.4. Elements  Learning rate  Neighborhood function Learning rate function

Self organizing maps 25 iCSC2014, Juan López González, University of Oviedo 2.5. Algorithm  Initialization  Input data preprocessing  Normalizing  Discrete-continuous variables?  Weight initialization  Random weights

Self organizing maps 26 iCSC2014, Juan López González, University of Oviedo 2.5. Algorithm (2)  Sampling  Take sample from input space  Matching  Find BMU: i.e. min of  Update weights  i.e.

Self organizing maps 27 iCSC2014, Juan López González, University of Oviedo 3. Practical exercise

Self organizing maps 28 iCSC2014, Juan López González, University of Oviedo 4.1. Digit recognition 4.2. Finish phonetics 4.3. Semantic map of word context 4. Map examples

Self organizing maps 29 iCSC2014, Juan López González, University of Oviedo 4.1. Digit recognition

Self organizing maps 30 iCSC2014, Juan López González, University of Oviedo 4.2. Finnish phonetics

Self organizing maps 31 iCSC2014, Juan López González, University of Oviedo 4.3. Semantic map of word context

Self organizing maps 32 iCSC2014, Juan López González, University of Oviedo 5.1. TASOM 5.2. GSOM 5.3. MuSOM 5. Other SOM based models

Self organizing maps 33 iCSC2014, Juan López González, University of Oviedo 5.1. TASOM  Time adaptative self-organizing maps  Deals with non-stationary input distributions  Adaptative learning rates: n(w,x)  Adaptative neighborhood rates : T(w,x)

Self organizing maps 34 iCSC2014, Juan López González, University of Oviedo 5.2. GSOM  Growing self-organizing maps  Deals with identifying sizes for SOMs  Spread factor  New nodes in boundaries  Good when unknown clusters

Self organizing maps 35 iCSC2014, Juan López González, University of Oviedo 5.3. MuSOM  Multimodal SOM  High level classification from sensory integration

Self organizing maps 36 iCSC2014, Juan López González, University of Oviedo Q & A