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Machine Learning

        Instructor: Rich Maclin
          rmaclin@d.umn.edu
  Text: Machine Learning, Mitchell
Notes based on Mitchell’s Lecture Notes
What is Learning?
Learning denotes changes in the system that are adaptive in
  the sense that they enable the system to do the same task or
  tasks drawn from the same population more effectively the
  next time. -- Simon, 1983

Learning is making useful changes in our minds. -- Minsky,
  1985

Learning is constructing or modifying representations of
  what is being experienced. -- McCarthy, 1968

Learning is improving automatically with experience. --
  Mitchell, 1997
CS 5751 Machine     Chapter 1 Intro to Machine Learning      2
Learning
Why Machine Learning?
• Data, Data, DATA!!!
     – Examples
          • World wide web
          • Human genome project
          • Business data (WalMart sales “baskets”)
     – Idea: sift heap of data for nuggets of knowledge
• Some tasks beyond programming
     – Example: driving
     – Idea: learn by doing/watching/practicing (like humans)
• Customizing software
     – Example: web browsing for news information
     – Idea: observe user tendencies and incorporate

CS 5751 Machine         Chapter 1 Intro to Machine Learning     3
Learning
Typical Data Analysis Task
  Patient103                    Patient103                           Patient103
           time=1                        time=2                               time=n

  Age: 23                       Age: 23                              Age: 23
  FirstPregnancy: no            FirstPregnancy: no                   FirstPregnancy: no
  Anemia: no                    Anemia: no                           Anemia: no
  Diabetes: no                  Diabetes: YES                        Diabetes: no
  PreviousPrematureBirth: no    PreviousPrematureBirth: no           PreviousPrematureBirth: no
  Ultrasound: ?                 Ultrasound: abnormal                 Ultrasound: ?
  Elective C-Section: ?         Elective C-Section: no               Elective C-Section: no
  Emergency C-Section: ?        Emergency C-Section: ?               Emergency C-Section: YES
  ...                           ...                                  ...


Given
     – 9714 patient records, each describing a pregnancy and a birth
     – Each patient record contains 215 features (some are unknown)
Learn to predict:
     – Characteristics of patients at high risk for Emergency C-Section


CS 5751 Machine                Chapter 1 Intro to Machine Learning                                4
Learning
Credit Risk Analysis
  Customer103                    Customer103                         Customer103
               time=10                        time=11                            time=n

  Years of credit: 9             Years of credit: 9                  Years of credit: 9
  Loan balance: $2,400           Loan balance: $3,250                Loan balance: $4,500
  Income: $52K                   Income: ?                           Income: ?
  Own House: Yes                 Own House: Yes                      Own House: Yes
  Other delinquent accts: 2      Other delinquent accts: 2           Other delinquent accts: 3
  Max billing cycles late: 3     Max billing cycles late: 4          Max billing cycles late: 6
  Profitable customer: ?         Profitable customer: ?              Profitable customer: No
  ...                            ...                                 ...


Rules learned from data:
     IF Other-Delinquent-Accounts > 2, AND
        Number-Delinquent-Billing-Cycles > 1
     THEN Profitable-Customer? = No   [Deny Credit Application]
     IF Other-Delinquent-Accounts == 0, AND
        ((Income > $30K) OR (Years-of-Credit > 3))
     THEN Profitable-Customer? = Yes [Accept Application]


CS 5751 Machine                Chapter 1 Intro to Machine Learning                           5
Learning
Analysis/Prediction Problems
• What kind of direct mail customers buy?
• What products will/won’t customers buy?
• What changes will cause a customer to leave a
  bank?
• What are the characteristics of a gene?
• Does a picture contain an object (does a picture of
  space contain a metereorite -- especially one
  heading towards us)?
• … Lots more

CS 5751 Machine   Chapter 1 Intro to Machine Learning   6
Learning
Tasks too Hard to Program




                                        ALVINN [Pomerleau] drives
                                          70 MPH on highways



CS 5751 Machine   Chapter 1 Intro to Machine Learning          7
Learning
Software that Customizes to User




CS 5751 Machine   Chapter 1 Intro to Machine Learning   8
Learning
Defining a Learning Problem
Learning = improving with experience at some task
     – improve over task T
     – with respect to performance measure P
     – based on experience E
Ex 1: Learn to play checkers
     T: play checkers
     P: % of games won
     E: opportunity to play self
Ex 2: Sell more CDs
     T: sell CDs
     P: # of CDs sold
     E: different locations/prices of CD
CS 5751 Machine      Chapter 1 Intro to Machine Learning   9
Learning
Key Questions
T: play checkers, sell CDs
P: % games won, # CDs sold

To generate machine learner need to know:
     – What experience?
          • Direct or indirect?
          • Learner controlled?
          • Is the experience representative?
     – What exactly should be learned?
     – How to represent the learning function?
     – What algorithm used to learn the learning function?

CS 5751 Machine          Chapter 1 Intro to Machine Learning   10
Learning
Types of Training Experience
Direct or indirect?
Direct - observable, measurable
     – sometimes difficult to obtain
          • Checkers - is a move the best move for a situation?

     – sometimes straightforward
          • Sell CDs - how many CDs sold on a day? (look at receipts)

Indirect - must be inferred from what is measurable
     – Checkers - value moves based on outcome of game
     – Credit assignment problem
CS 5751 Machine          Chapter 1 Intro to Machine Learning            11
Learning
Types of Training Experience (cont)
Who controls?
     – Learner - what is best move at each point?
       (Exploitation/Exploration)
     – Teacher - is teacher’s move the best? (Do we want to
       just emulate the teachers moves??)

BIG Question: is experience representative of
  performance goal?
     – If Checkers learner only plays itself will it be able to
       play humans?
     – What if results from CD seller influenced by factors not
       measured (holiday shopping, weather, etc.)?

CS 5751 Machine      Chapter 1 Intro to Machine Learning      12
Learning
Choosing Target Function
Checkers - what does learner do - make moves
     ChooseMove - select move based on board
          ChooseMove : Board → Move
          V : Board → ℜ
     ChooseMove(b): from b pick move with highest value
     But how do we define V(b) for boards b?
     Possible definition:
          V(b) = 100 if b is a final board state of a win
          V(b) = -100 if b is a final board state of a loss
          V(b) = 0 if b is a final board state of a draw
          if b not final state, V(b) =V(b´) where b´ is best final board
             reached by starting at b and playing optimally from there
          Correct, but not operational

CS 5751 Machine          Chapter 1 Intro to Machine Learning               13
Learning
Representation of Target Function
• Collection of rules?
     IF double jump available THEN
      make double jump

• Neural network?
• Polynomial function of problem features?

      w0 + w1 # blackPieces (b) + w2 # redPieces(b) +
      w3 # blackKings (b) + w4 # redKings (b) +
      w5 # redThreatened (b) + w6 # blackThreatened (b)

CS 5751 Machine    Chapter 1 Intro to Machine Learning   14
Learning
Obtaining Training Examples
V (b) : the true target function
 ˆ
V (b) : the learned function
Vtrain (b) : the training value


One rule for estimating training values :
             ˆ
 V (b) ← V ( Successor (b))
     train




CS 5751 Machine   Chapter 1 Intro to Machine Learning   15
Learning
Choose Weight Tuning Rule
LMS Weight update rule:
   Do repeatedly :
    Select a training example b at random
     1. Compute error (b) :
                                       ˆ
                  error (b) = V (b) − V (b)
                                     train

      2. For each board feature f i , update weight wi :
                   wi ← wi + c × f i × error (b)
          c is some small constant, say 0.1, to moderate
          rate of learning

CS 5751 Machine      Chapter 1 Intro to Machine Learning   16
Learning
Design Choices
                                   Determining Type of
                                   Training Experience
    Games against expert                                               Table of correct moves
                                             Games against self
                            Determining
                           Target Function
       Board       Move                           Board     Value

                                              Determining Representation
                                                 of Learned Function
                      Linear function of features                               Neural Network

                                  Determining
                               Learning Algorithm
                      Gradient Descent                            Linear Programming

                                Completed Design


CS 5751 Machine               Chapter 1 Intro to Machine Learning                               17
Learning
Some Areas of Machine Learning
• Inductive Learning: inferring new knowledge
  from observations (not guaranteed correct)
     – Concept/Classification Learning - identify
       characteristics of class members (e.g., what makes a CS
       class fun, what makes a customer buy, etc.)
     – Unsupervised Learning - examine data to infer new
       characteristics (e.g., break chemicals into similar
       groups, infer new mathematical rule, etc.)
     – Reinforcement Learning - learn appropriate moves to
       achieve delayed goal (e.g., win a game of Checkers,
       perform a robot task, etc.)
• Deductive Learning: recombine existing
  knowledge to more effectively solve problems
CS 5751 Machine      Chapter 1 Intro to Machine Learning    18
Learning
Classification/Concept Learning




• What characteristic(s) predict a smile?
     – Variation on Sesame Street game: why are these things a lot like
       the others (or not)?
• ML Approach: infer model (characteristics that indicate) of
  why a face is/is not smiling
CS 5751 Machine         Chapter 1 Intro to Machine Learning               19
Learning
Unsupervised Learning




• Clustering - group points into “classes”
• Other ideas:
     – look for mathematical relationships between features
     – look for anomalies in data bases (data that does not fit)
CS 5751 Machine          Chapter 1 Intro to Machine Learning       20
Learning
Reinforcement Learning
                    Problem                                    Policy
                   G      S - start
                          G - goal
                          Possible actions:
                             up     left
S                            down right

• Problem: feedback (reinforcements) are delayed - how to
  value intermediate (no goal states)
• Idea: online dynamic programming to produce policy
  function
• Policy: action taken leads to highest future reinforcement
  (if policy followed)
CS 5751 Machine          Chapter 1 Intro to Machine Learning            21
Learning
Analytical Learning
                                                   Problem!
                  S1       S2           S3        Backtrack!


        Init               S4           S5           S6        Goal


                           S7           S8


                                        S9           S0




• During search processes (planning, etc.) remember work
  involved in solving tough problems
• Reuse the acquired knowledge when presented with
  similar problems in the future (avoid bad decisions)

CS 5751 Machine        Chapter 1 Intro to Machine Learning            22
Learning
The Present in Machine Learning
The tip of the iceberg:
• First-generation algorithms: neural nets, decision
  trees, regression, support vector machines, …
• Composite algorithms - ensembles
• Some work on assessing effectiveness, limits
• Applied to simple data bases
• Budding industry (especially in data mining)



CS 5751 Machine   Chapter 1 Intro to Machine Learning   23
Learning
The Future of Machine Learning
Lots of areas of impact:
• Learn across multiple data bases, as well as web
  and news feeds
• Learn across multi-media data
• Cumulative, lifelong learning
• Agents with learning embedded
• Programming languages with learning embedded?
• Learning by active experimentation


CS 5751 Machine   Chapter 1 Intro to Machine Learning   24
Learning
What is Data Mining?
• Depends on who you ask
• General idea: the analysis of large amounts of data
  (and therefore efficiency is an issue)
• Interfaces several areas, notably machine learning
  and database systems
• Lots of perspectives:
     – ML: learning where efficiency matters
     – DBMS: extended techniques for analysis of raw data,
       automatic production of knowledge
• What is all the hubbub?
     – Companies make lots of money with it (e.g., WalMart)
CS 5751 Machine       Chapter 1 Intro to Machine Learning    25
Learning
Related Disciplines
•   Artificial Intelligence
•   Statistics
•   Psychology and neurobiology
•   Philosophy
•   Computational complexity theory
•   Control theory
•   Information theory
•   Database Systems
•   ...

CS 5751 Machine      Chapter 1 Intro to Machine Learning   26
Learning
Issues in Machine Learning
• What algorithms can approximate functions well
  (and when)?
• How does number of training examples influence
  accuracy?
• How does complexity of hypothesis representation
  impact it?
• How does noisy data influence accuracy?
• What are the theoretical limits of learnability?
• How can prior knowledge of learner help?
• What clues can we get from biological learning
  systems?
CS 5751 Machine   Chapter 1 Intro to Machine Learning   27
Learning

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Microsoft PowerPoint - Chapter01

  • 1. Machine Learning Instructor: Rich Maclin rmaclin@d.umn.edu Text: Machine Learning, Mitchell Notes based on Mitchell’s Lecture Notes
  • 2. What is Learning? Learning denotes changes in the system that are adaptive in the sense that they enable the system to do the same task or tasks drawn from the same population more effectively the next time. -- Simon, 1983 Learning is making useful changes in our minds. -- Minsky, 1985 Learning is constructing or modifying representations of what is being experienced. -- McCarthy, 1968 Learning is improving automatically with experience. -- Mitchell, 1997 CS 5751 Machine Chapter 1 Intro to Machine Learning 2 Learning
  • 3. Why Machine Learning? • Data, Data, DATA!!! – Examples • World wide web • Human genome project • Business data (WalMart sales “baskets”) – Idea: sift heap of data for nuggets of knowledge • Some tasks beyond programming – Example: driving – Idea: learn by doing/watching/practicing (like humans) • Customizing software – Example: web browsing for news information – Idea: observe user tendencies and incorporate CS 5751 Machine Chapter 1 Intro to Machine Learning 3 Learning
  • 4. Typical Data Analysis Task Patient103 Patient103 Patient103 time=1 time=2 time=n Age: 23 Age: 23 Age: 23 FirstPregnancy: no FirstPregnancy: no FirstPregnancy: no Anemia: no Anemia: no Anemia: no Diabetes: no Diabetes: YES Diabetes: no PreviousPrematureBirth: no PreviousPrematureBirth: no PreviousPrematureBirth: no Ultrasound: ? Ultrasound: abnormal Ultrasound: ? Elective C-Section: ? Elective C-Section: no Elective C-Section: no Emergency C-Section: ? Emergency C-Section: ? Emergency C-Section: YES ... ... ... Given – 9714 patient records, each describing a pregnancy and a birth – Each patient record contains 215 features (some are unknown) Learn to predict: – Characteristics of patients at high risk for Emergency C-Section CS 5751 Machine Chapter 1 Intro to Machine Learning 4 Learning
  • 5. Credit Risk Analysis Customer103 Customer103 Customer103 time=10 time=11 time=n Years of credit: 9 Years of credit: 9 Years of credit: 9 Loan balance: $2,400 Loan balance: $3,250 Loan balance: $4,500 Income: $52K Income: ? Income: ? Own House: Yes Own House: Yes Own House: Yes Other delinquent accts: 2 Other delinquent accts: 2 Other delinquent accts: 3 Max billing cycles late: 3 Max billing cycles late: 4 Max billing cycles late: 6 Profitable customer: ? Profitable customer: ? Profitable customer: No ... ... ... Rules learned from data: IF Other-Delinquent-Accounts > 2, AND Number-Delinquent-Billing-Cycles > 1 THEN Profitable-Customer? = No [Deny Credit Application] IF Other-Delinquent-Accounts == 0, AND ((Income > $30K) OR (Years-of-Credit > 3)) THEN Profitable-Customer? = Yes [Accept Application] CS 5751 Machine Chapter 1 Intro to Machine Learning 5 Learning
  • 6. Analysis/Prediction Problems • What kind of direct mail customers buy? • What products will/won’t customers buy? • What changes will cause a customer to leave a bank? • What are the characteristics of a gene? • Does a picture contain an object (does a picture of space contain a metereorite -- especially one heading towards us)? • … Lots more CS 5751 Machine Chapter 1 Intro to Machine Learning 6 Learning
  • 7. Tasks too Hard to Program ALVINN [Pomerleau] drives 70 MPH on highways CS 5751 Machine Chapter 1 Intro to Machine Learning 7 Learning
  • 8. Software that Customizes to User CS 5751 Machine Chapter 1 Intro to Machine Learning 8 Learning
  • 9. Defining a Learning Problem Learning = improving with experience at some task – improve over task T – with respect to performance measure P – based on experience E Ex 1: Learn to play checkers T: play checkers P: % of games won E: opportunity to play self Ex 2: Sell more CDs T: sell CDs P: # of CDs sold E: different locations/prices of CD CS 5751 Machine Chapter 1 Intro to Machine Learning 9 Learning
  • 10. Key Questions T: play checkers, sell CDs P: % games won, # CDs sold To generate machine learner need to know: – What experience? • Direct or indirect? • Learner controlled? • Is the experience representative? – What exactly should be learned? – How to represent the learning function? – What algorithm used to learn the learning function? CS 5751 Machine Chapter 1 Intro to Machine Learning 10 Learning
  • 11. Types of Training Experience Direct or indirect? Direct - observable, measurable – sometimes difficult to obtain • Checkers - is a move the best move for a situation? – sometimes straightforward • Sell CDs - how many CDs sold on a day? (look at receipts) Indirect - must be inferred from what is measurable – Checkers - value moves based on outcome of game – Credit assignment problem CS 5751 Machine Chapter 1 Intro to Machine Learning 11 Learning
  • 12. Types of Training Experience (cont) Who controls? – Learner - what is best move at each point? (Exploitation/Exploration) – Teacher - is teacher’s move the best? (Do we want to just emulate the teachers moves??) BIG Question: is experience representative of performance goal? – If Checkers learner only plays itself will it be able to play humans? – What if results from CD seller influenced by factors not measured (holiday shopping, weather, etc.)? CS 5751 Machine Chapter 1 Intro to Machine Learning 12 Learning
  • 13. Choosing Target Function Checkers - what does learner do - make moves ChooseMove - select move based on board ChooseMove : Board → Move V : Board → ℜ ChooseMove(b): from b pick move with highest value But how do we define V(b) for boards b? Possible definition: V(b) = 100 if b is a final board state of a win V(b) = -100 if b is a final board state of a loss V(b) = 0 if b is a final board state of a draw if b not final state, V(b) =V(b´) where b´ is best final board reached by starting at b and playing optimally from there Correct, but not operational CS 5751 Machine Chapter 1 Intro to Machine Learning 13 Learning
  • 14. Representation of Target Function • Collection of rules? IF double jump available THEN make double jump • Neural network? • Polynomial function of problem features? w0 + w1 # blackPieces (b) + w2 # redPieces(b) + w3 # blackKings (b) + w4 # redKings (b) + w5 # redThreatened (b) + w6 # blackThreatened (b) CS 5751 Machine Chapter 1 Intro to Machine Learning 14 Learning
  • 15. Obtaining Training Examples V (b) : the true target function ˆ V (b) : the learned function Vtrain (b) : the training value One rule for estimating training values : ˆ V (b) ← V ( Successor (b)) train CS 5751 Machine Chapter 1 Intro to Machine Learning 15 Learning
  • 16. Choose Weight Tuning Rule LMS Weight update rule: Do repeatedly : Select a training example b at random 1. Compute error (b) : ˆ error (b) = V (b) − V (b) train 2. For each board feature f i , update weight wi : wi ← wi + c × f i × error (b) c is some small constant, say 0.1, to moderate rate of learning CS 5751 Machine Chapter 1 Intro to Machine Learning 16 Learning
  • 17. Design Choices Determining Type of Training Experience Games against expert Table of correct moves Games against self Determining Target Function Board Move Board Value Determining Representation of Learned Function Linear function of features Neural Network Determining Learning Algorithm Gradient Descent Linear Programming Completed Design CS 5751 Machine Chapter 1 Intro to Machine Learning 17 Learning
  • 18. Some Areas of Machine Learning • Inductive Learning: inferring new knowledge from observations (not guaranteed correct) – Concept/Classification Learning - identify characteristics of class members (e.g., what makes a CS class fun, what makes a customer buy, etc.) – Unsupervised Learning - examine data to infer new characteristics (e.g., break chemicals into similar groups, infer new mathematical rule, etc.) – Reinforcement Learning - learn appropriate moves to achieve delayed goal (e.g., win a game of Checkers, perform a robot task, etc.) • Deductive Learning: recombine existing knowledge to more effectively solve problems CS 5751 Machine Chapter 1 Intro to Machine Learning 18 Learning
  • 19. Classification/Concept Learning • What characteristic(s) predict a smile? – Variation on Sesame Street game: why are these things a lot like the others (or not)? • ML Approach: infer model (characteristics that indicate) of why a face is/is not smiling CS 5751 Machine Chapter 1 Intro to Machine Learning 19 Learning
  • 20. Unsupervised Learning • Clustering - group points into “classes” • Other ideas: – look for mathematical relationships between features – look for anomalies in data bases (data that does not fit) CS 5751 Machine Chapter 1 Intro to Machine Learning 20 Learning
  • 21. Reinforcement Learning Problem Policy G S - start G - goal Possible actions: up left S down right • Problem: feedback (reinforcements) are delayed - how to value intermediate (no goal states) • Idea: online dynamic programming to produce policy function • Policy: action taken leads to highest future reinforcement (if policy followed) CS 5751 Machine Chapter 1 Intro to Machine Learning 21 Learning
  • 22. Analytical Learning Problem! S1 S2 S3 Backtrack! Init S4 S5 S6 Goal S7 S8 S9 S0 • During search processes (planning, etc.) remember work involved in solving tough problems • Reuse the acquired knowledge when presented with similar problems in the future (avoid bad decisions) CS 5751 Machine Chapter 1 Intro to Machine Learning 22 Learning
  • 23. The Present in Machine Learning The tip of the iceberg: • First-generation algorithms: neural nets, decision trees, regression, support vector machines, … • Composite algorithms - ensembles • Some work on assessing effectiveness, limits • Applied to simple data bases • Budding industry (especially in data mining) CS 5751 Machine Chapter 1 Intro to Machine Learning 23 Learning
  • 24. The Future of Machine Learning Lots of areas of impact: • Learn across multiple data bases, as well as web and news feeds • Learn across multi-media data • Cumulative, lifelong learning • Agents with learning embedded • Programming languages with learning embedded? • Learning by active experimentation CS 5751 Machine Chapter 1 Intro to Machine Learning 24 Learning
  • 25. What is Data Mining? • Depends on who you ask • General idea: the analysis of large amounts of data (and therefore efficiency is an issue) • Interfaces several areas, notably machine learning and database systems • Lots of perspectives: – ML: learning where efficiency matters – DBMS: extended techniques for analysis of raw data, automatic production of knowledge • What is all the hubbub? – Companies make lots of money with it (e.g., WalMart) CS 5751 Machine Chapter 1 Intro to Machine Learning 25 Learning
  • 26. Related Disciplines • Artificial Intelligence • Statistics • Psychology and neurobiology • Philosophy • Computational complexity theory • Control theory • Information theory • Database Systems • ... CS 5751 Machine Chapter 1 Intro to Machine Learning 26 Learning
  • 27. Issues in Machine Learning • What algorithms can approximate functions well (and when)? • How does number of training examples influence accuracy? • How does complexity of hypothesis representation impact it? • How does noisy data influence accuracy? • What are the theoretical limits of learnability? • How can prior knowledge of learner help? • What clues can we get from biological learning systems? CS 5751 Machine Chapter 1 Intro to Machine Learning 27 Learning