Data Mining Project

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ITS632_Chapter5_Lesson.ppt

Data Mining
Classification: Alternative Techniques

Lecture Notes for Chapter 5

Introduction to Data Mining

by

Tan, Steinbach, Kumar

© Tan,Steinbach, Kumar Introduction to Data Mining 4/18/2004 *

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Rule-Based Classifier

  • Classify records by using a collection of “if…then…” rules

  • Rule: (Condition)  y
  • where
  • Condition is a conjunctions of attributes
  • y is the class label
  • LHS: rule antecedent or condition
  • RHS: rule consequent
  • Examples of classification rules:
  • (Blood Type=Warm)  (Lay Eggs=Yes)  Birds
  • (Taxable Income < 50K)  (Refund=Yes)  Evade=No

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Rule-based Classifier (Example)

R1: (Give Birth = no)  (Can Fly = yes)  Birds

R2: (Give Birth = no)  (Live in Water = yes)  Fishes

R3: (Give Birth = yes)  (Blood Type = warm)  Mammals

R4: (Give Birth = no)  (Can Fly = no)  Reptiles

R5: (Live in Water = sometimes)  Amphibians

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Application of Rule-Based Classifier

  • A rule r covers an instance x if the attributes of the instance satisfy the condition of the rule

R1: (Give Birth = no)  (Can Fly = yes)  Birds

R2: (Give Birth = no)  (Live in Water = yes)  Fishes

R3: (Give Birth = yes)  (Blood Type = warm)  Mammals

R4: (Give Birth = no)  (Can Fly = no)  Reptiles

R5: (Live in Water = sometimes)  Amphibians

The rule R1 covers a hawk => Bird

The rule R3 covers the grizzly bear => Mammal

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Rule Coverage and Accuracy

  • Coverage of a rule:
  • Fraction of records that satisfy the antecedent of a rule
  • Accuracy of a rule:
  • Fraction of records that satisfy both the antecedent and consequent of a rule

(Status=Single)  No

Coverage = 40%, Accuracy = 50%

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Tid

Refund

Marital

Status

Taxable

Income

Class

1

Yes

Single

125K

No

2

No

Married

100K

No

3

No

Single

70K

No

4

Yes

Married

120K

No

5

No

Divorced

95K

Yes

6

No

Married

60K

No

7

Yes

Divorced

220K

No

8

No

Single

85K

Yes

9

No

Married

75K

No

10

No

Single

90K

Yes

10

How does Rule-based Classifier Work?

R1: (Give Birth = no)  (Can Fly = yes)  Birds

R2: (Give Birth = no)  (Live in Water = yes)  Fishes

R3: (Give Birth = yes)  (Blood Type = warm)  Mammals

R4: (Give Birth = no)  (Can Fly = no)  Reptiles

R5: (Live in Water = sometimes)  Amphibians

A lemur triggers rule R3, so it is classified as a mammal

A turtle triggers both R4 and R5

A dogfish shark triggers none of the rules

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Characteristics of Rule-Based Classifier

  • Mutually exclusive rules
  • Classifier contains mutually exclusive rules if the rules are independent of each other
  • Every record is covered by at most one rule
  • Exhaustive rules
  • Classifier has exhaustive coverage if it accounts for every possible combination of attribute values
  • Each record is covered by at least one rule

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

From Decision Trees To Rules

Rules are mutually exclusive and exhaustive

Rule set contains as much information as the tree

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Rules Can Be Simplified

Initial Rule: (Refund=No)  (Status=Married)  No

Simplified Rule: (Status=Married)  No

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Tid

Refund

Marital

Status

Taxable

Income

Cheat

1

Yes

Single

125K

No

2

No

Married

100K

No

3

No

Single

70K

No

4

Yes

Married

120K

No

5

No

Divorced

95K

Yes

6

No

Married

60K

No

7

Yes

Divorced

220K

No

8

No

Single

85K

Yes

9

No

Married

75K

No

10

No

Single

90K

Yes

10

Effect of Rule Simplification

  • Rules are no longer mutually exclusive
  • A record may trigger more than one rule
  • Solution?
  • Ordered rule set
  • Unordered rule set – use voting schemes
  • Rules are no longer exhaustive
  • A record may not trigger any rules
  • Solution?
  • Use a default class

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Ordered Rule Set

  • Rules are rank ordered according to their priority
  • An ordered rule set is known as a decision list
  • When a test record is presented to the classifier
  • It is assigned to the class label of the highest ranked rule it has triggered
  • If none of the rules fired, it is assigned to the default class

R1: (Give Birth = no)  (Can Fly = yes)  Birds

R2: (Give Birth = no)  (Live in Water = yes)  Fishes

R3: (Give Birth = yes)  (Blood Type = warm)  Mammals

R4: (Give Birth = no)  (Can Fly = no)  Reptiles

R5: (Live in Water = sometimes)  Amphibians

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Rule Ordering Schemes

  • Rule-based ordering
  • Individual rules are ranked based on their quality
  • Class-based ordering
  • Rules that belong to the same class appear together

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Rule-based Ordering (Refund=Yes) ==> No (Refund=No, Marital Status={Single,Divorced}, Taxable Income<80K) ==> No (Refund=No, Marital Status={Single,Divorced}, Taxable Income>80K) ==> Yes (Refund=No, Marital Status={Married}) ==> No �

Class-based Ordering (Refund=Yes) ==> No (Refund=No, Marital Status={Single,Divorced}, Taxable Income<80K) ==> No (Refund=No, Marital Status={Married}) ==> No (Refund=No, Marital Status={Single,Divorced}, Taxable Income>80K) ==> Yes �

Building Classification Rules

  • Direct Method:
  • Extract rules directly from data
  • e.g.: RIPPER, CN2, Holte’s 1R
  • Indirect Method:
  • Extract rules from other classification models (e.g.
    decision trees, neural networks, etc).
  • e.g: C4.5rules

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Direct Method: Sequential Covering

Start from an empty rule

Grow a rule using the Learn-One-Rule function

Remove training records covered by the rule

Repeat Step (2) and (3) until stopping criterion is met

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Example of Sequential Covering

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Example of Sequential Covering…

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Aspects of Sequential Covering

  • Rule Growing
  • Instance Elimination
  • Rule Evaluation
  • Stopping Criterion
  • Rule Pruning

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Rule Growing

  • Two common strategies

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

(a) General-to-specific�

Refund= No�

Status = Single�

Status = Divorced�

Status = Married�

Income �> 80K �

...�

{ }�

Yes: 0 No: 3�

Yes: 3 No: 4�

Yes: 3 No: 4�

Yes: 2 No: 1�

Yes: 1 No: 0�

Yes: 3 No: 1�

Refund=No,�Status=Single,�Income=85K (Class=Yes)�

Refund=No,�Status=Single,�Income=90K (Class=Yes)�

Refund=No,�Status = Single�(Class = Yes)�

(b) Specific-to-general�

Rule Growing (Examples)

  • CN2 Algorithm:
  • Start from an empty conjunct: {}
  • Add conjuncts that minimizes the entropy measure: {A}, {A,B}, …
  • Determine the rule consequent by taking majority class of instances covered by the rule
  • RIPPER Algorithm:
  • Start from an empty rule: {} => class
  • Add conjuncts that maximizes FOIL’s information gain measure:
  • R0: {} => class (initial rule)
  • R1: {A} => class (rule after adding conjunct)
  • Gain(R0, R1) = t [ log (p1/(p1+n1)) – log (p0/(p0 + n0)) ]
  • where t: number of positive instances covered by both R0 and R1

p0: number of positive instances covered by R0

n0: number of negative instances covered by R0

p1: number of positive instances covered by R1

n1: number of negative instances covered by R1

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Instance Elimination

  • Why do we need to eliminate instances?
  • Otherwise, the next rule is identical to previous rule
  • Why do we remove positive instances?
  • Ensure that the next rule is different
  • Why do we remove negative instances?
  • Prevent underestimating accuracy of rule
  • Compare rules R2 and R3 in the diagram

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

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Rule Evaluation

  • Metrics:
  • Accuracy
  • Laplace

  • M-estimate

n : Number of instances covered by rule

nc : Number of instances covered by rule

k : Number of classes

p : Prior probability

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Stopping Criterion and Rule Pruning

  • Stopping criterion
  • Compute the gain
  • If gain is not significant, discard the new rule
  • Rule Pruning
  • Similar to post-pruning of decision trees
  • Reduced Error Pruning:
  • Remove one of the conjuncts in the rule
  • Compare error rate on validation set before and after pruning
  • If error improves, prune the conjunct

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Summary of Direct Method

  • Grow a single rule
  • Remove Instances from rule
  • Prune the rule (if necessary)
  • Add rule to Current Rule Set
  • Repeat

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Direct Method: RIPPER

  • For 2-class problem, choose one of the classes as positive class, and the other as negative class
  • Learn rules for positive class
  • Negative class will be default class
  • For multi-class problem
  • Order the classes according to increasing class prevalence (fraction of instances that belong to a particular class)
  • Learn the rule set for smallest class first, treat the rest as negative class
  • Repeat with next smallest class as positive class

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Direct Method: RIPPER

  • Growing a rule:
  • Start from empty rule
  • Add conjuncts as long as they improve FOIL’s information gain
  • Stop when rule no longer covers negative examples
  • Prune the rule immediately using incremental reduced error pruning
  • Measure for pruning: v = (p-n)/(p+n)
  • p: number of positive examples covered by the rule in
    the validation set
  • n: number of negative examples covered by the rule in
    the validation set
  • Pruning method: delete any final sequence of conditions that maximizes v

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Direct Method: RIPPER

  • Building a Rule Set:
  • Use sequential covering algorithm
  • Finds the best rule that covers the current set of positive examples
  • Eliminate both positive and negative examples covered by the rule
  • Each time a rule is added to the rule set, compute the new description length
  • stop adding new rules when the new description length is d bits longer than the smallest description length obtained so far

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Direct Method: RIPPER

  • Optimize the rule set:
  • For each rule r in the rule set R
  • Consider 2 alternative rules:

Replacement rule (r*): grow new rule from scratch

Revised rule(r’): add conjuncts to extend the rule r

  • Compare the rule set for r against the rule set for r*
    and r’
  • Choose rule set that minimizes MDL principle
  • Repeat rule generation and rule optimization for the remaining positive examples

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Indirect Methods

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

P�

Rule Set r1: (P=No,Q=No) ==> - r2: (P=No,Q=Yes) ==> + r3: (P=Yes,R=No) ==> + r4: (P=Yes,R=Yes,Q=No) ==> - r5: (P=Yes,R=Yes,Q=Yes) ==> +�

Q�

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-�

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Yes�

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Indirect Method: C4.5rules

  • Extract rules from an unpruned decision tree
  • For each rule, r: A  y,
  • consider an alternative rule r’: A’  y where A’ is obtained by removing one of the conjuncts in A
  • Compare the pessimistic error rate for r against all r’s
  • Prune if one of the r’s has lower pessimistic error rate
  • Repeat until we can no longer improve generalization error

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Indirect Method: C4.5rules

  • Instead of ordering the rules, order subsets of rules (class ordering)
  • Each subset is a collection of rules with the same rule consequent (class)
  • Compute description length of each subset
  • Description length = L(error) + g L(model)
  • g is a parameter that takes into account the presence of redundant attributes in a rule set
    (default value = 0.5)

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Example

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

animals2

Name Give Birth Lay Eggs Can Fly Live in Water Have Legs Class
human yes no no no yes mammals
python no yes no no no reptiles
salmon no yes no yes no fishes
whale yes no no yes no mammals
frog no yes no sometimes yes amphibians
komodo no yes no no yes reptiles
bat yes no yes no yes mammals
pigeon no yes yes no yes birds
cat yes no no no yes mammals
leopard shark yes no no yes no fishes
turtle no yes no sometimes yes reptiles
penguin no yes no sometimes yes birds
porcupine yes no no no yes mammals
eel no yes no yes no fishes
salamander no yes no sometimes yes amphibians
gila monster no yes no no yes reptiles
platypus no yes no no yes mammals
owl no yes yes no yes birds
dolphin yes no no yes no mammals
eagle no yes yes no yes birds

C4.5 versus C4.5rules versus RIPPER

C4.5rules:

(Give Birth=No, Can Fly=Yes)  Birds

(Give Birth=No, Live in Water=Yes)  Fishes

(Give Birth=Yes)  Mammals

(Give Birth=No, Can Fly=No, Live in Water=No)  Reptiles

( )  Amphibians

RIPPER:

(Live in Water=Yes)  Fishes

(Have Legs=No)  Reptiles

(Give Birth=No, Can Fly=No, Live In Water=No)
 Reptiles

(Can Fly=Yes,Give Birth=No)  Birds

()  Mammals

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

C4.5 versus C4.5rules versus RIPPER

C4.5 and C4.5rules:

RIPPER:

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Sheet1

PREDICTED CLASS
Amphibians Fishes Reptiles Birds Mammals
ACTUAL Amphibians 0 0 0 0 2
CLASS Fishes 0 3 0 0 0
Reptiles 0 0 3 0 1
Birds 0 0 1 2 1
Mammals 0 2 1 0 4
C4.5 Amphibians Fishes Reptiles Birds Mammals
Amphibians 2 0 0 0 0
Fishes 0 2 0 0 1
Reptiles 1 0 3 0 0
Birds 1 0 0 3 0
Mammals 0 0 1 0 6
C4.5rules Amphibians Fishes Reptiles Birds Mammals
Amphibians 2 0 0 0 0
Fishes 0 2 0 0 1
Reptiles 1 0 3 0 0
Birds 1 0 0 3 0
Mammals 0 0 1 0 6

Sheet2

Sheet3

Sheet1

RIPPER: Amphibians Fishes Reptiles Birds Mammals
Amphibians 0 0 0 0 2
Fishes 0 3 0 0 0
Reptiles 0 0 3 0 1
Birds 0 0 1 2 1
Mammals 0 2 1 0 4
PREDICTED CLASS
Amphibians Fishes Reptiles Birds Mammals
ACTUAL Amphibians 2 0 0 0 0
CLASS Fishes 0 2 0 0 1
Reptiles 1 0 3 0 0
Birds 1 0 0 3 0
Mammals 0 0 1 0 6
C4.5rules Amphibians Fishes Reptiles Birds Mammals
Amphibians 2 0 0 0 0
Fishes 0 2 0 0 1
Reptiles 1 0 3 0 0
Birds 1 0 0 3 0
Mammals 0 0 1 0 6

Sheet2

Sheet3

Advantages of Rule-Based Classifiers

  • As highly expressive as decision trees
  • Easy to interpret
  • Easy to generate
  • Can classify new instances rapidly
  • Performance comparable to decision trees

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Instance-Based Classifiers

  • Store the training records
  • Use training records to
    predict the class label of
    unseen cases

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Instance Based Classifiers

  • Examples:
  • Rote-learner
  • Memorizes entire training data and performs classification only if attributes of record match one of the training examples exactly
  • Nearest neighbor
  • Uses k “closest” points (nearest neighbors) for performing classification

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Nearest Neighbor Classifiers

  • Basic idea:
  • If it walks like a duck, quacks like a duck, then it’s probably a duck

Training Records

Test Record

Compute Distance

Choose k of the “nearest” records

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Nearest-Neighbor Classifiers

  • Requires three things
  • The set of stored records
  • Distance Metric to compute distance between records
  • The value of k, the number of nearest neighbors to retrieve
  • To classify an unknown record:
  • Compute distance to other training records
  • Identify k nearest neighbors
  • Use class labels of nearest neighbors to determine the class label of unknown record (e.g., by taking majority vote)

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Unknown record�

Definition of Nearest Neighbor

K-nearest neighbors of a record x are data points that have the k smallest distance to x

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

1 nearest-neighbor

Voronoi Diagram

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Nearest Neighbor Classification

  • Compute distance between two points:
  • Euclidean distance

  • Determine the class from nearest neighbor list
  • take the majority vote of class labels among the k-nearest neighbors
  • Weigh the vote according to distance
  • weight factor, w = 1/d2

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Nearest Neighbor Classification…

  • Choosing the value of k:
  • If k is too small, sensitive to noise points
  • If k is too large, neighborhood may include points from other classes

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

X�

Nearest Neighbor Classification…

  • Scaling issues
  • Attributes may have to be scaled to prevent distance measures from being dominated by one of the attributes
  • Example:
  • height of a person may vary from 1.5m to 1.8m
  • weight of a person may vary from 90lb to 300lb
  • income of a person may vary from $10K to $1M

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Nearest Neighbor Classification…

  • Problem with Euclidean measure:
  • High dimensional data
  • curse of dimensionality
  • Can produce counter-intuitive results

1 1 1 1 1 1 1 1 1 1 1 0

0 1 1 1 1 1 1 1 1 1 1 1

1 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 1

vs

d = 1.4142

d = 1.4142

  • Solution: Normalize the vectors to unit length

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Nearest neighbor Classification…

  • k-NN classifiers are lazy learners
  • It does not build models explicitly
  • Unlike eager learners such as decision tree induction and rule-based systems
  • Classifying unknown records are relatively expensive

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Example: PEBLS

  • PEBLS: Parallel Examplar-Based Learning System (Cost & Salzberg)
  • Works with both continuous and nominal features
  • For nominal features, distance between two nominal values is computed using modified value difference metric (MVDM)
  • Each record is assigned a weight factor
  • Number of nearest neighbor, k = 1

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Example: PEBLS

Distance between nominal attribute values:

d(Single,Married)

= | 2/4 – 0/4 | + | 2/4 – 4/4 | = 1

d(Single,Divorced)

= | 2/4 – 1/2 | + | 2/4 – 1/2 | = 0

d(Married,Divorced)

= | 0/4 – 1/2 | + | 4/4 – 1/2 | = 1

d(Refund=Yes,Refund=No)

= | 0/3 – 3/7 | + | 3/3 – 4/7 | = 6/7

Class Marital Status
Single Married Divorced
Yes 2 0 1
No 2 4 1
Class Refund
Yes No
Yes 0 3
No 3 4

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Tid

Refund

Marital

Status

Taxable

Income

Cheat

1

Yes

Single

125K

No

2

No

Married

100K

No

3

No

Single

70K

No

4

Yes

Married

120K

No

5

No

Divorced

95K

Yes

6

No

Married

60K

No

7

Yes

Divorced

220K

No

8

No

Single

85K

Yes

9

No

Married

75K

No

10

No

Single

90K

Yes

10

Example: PEBLS

Distance between record X and record Y:

where:

wX  1 if X makes accurate prediction most of the time

wX > 1 if X is not reliable for making predictions

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Tid

Refund

Marital

Status

Taxable

Income

Cheat

X

Yes

Single

125K

No

Y

No

Married

100K

No

10

Bayes Classifier

  • A probabilistic framework for solving classification problems
  • Conditional Probability:
  • Bayes theorem:

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Example of Bayes Theorem

  • Given:
  • A doctor knows that meningitis causes stiff neck 50% of the time
  • Prior probability of any patient having meningitis is 1/50,000
  • Prior probability of any patient having stiff neck is 1/20

  • If a patient has stiff neck, what’s the probability he/she has meningitis?

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Bayesian Classifiers

  • Consider each attribute and class label as random variables

  • Given a record with attributes (A1, A2,…,An)
  • Goal is to predict class C
  • Specifically, we want to find the value of C that maximizes P(C| A1, A2,…,An )
  • Can we estimate P(C| A1, A2,…,An ) directly from data?

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Bayesian Classifiers

  • Approach:
  • compute the posterior probability P(C | A1, A2, …, An) for all values of C using the Bayes theorem

  • Choose value of C that maximizes
    P(C | A1, A2, …, An)
  • Equivalent to choosing value of C that maximizes
    P(A1, A2, …, An|C) P(C)

  • How to estimate P(A1, A2, …, An | C )?

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Naïve Bayes Classifier

  • Assume independence among attributes Ai when class is given:
  • P(A1, A2, …, An |C) = P(A1| Cj) P(A2| Cj)… P(An| Cj)

  • Can estimate P(Ai| Cj) for all Ai and Cj.

  • New point is classified to Cj if P(Cj)  P(Ai| Cj) is maximal.

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How to Estimate Probabilities from Data?

  • Class: P(C) = Nc/N
  • e.g., P(No) = 7/10,
    P(Yes) = 3/10

  • For discrete attributes:

    P(Ai | Ck) = |Aik|/ Nc
  • where |Aik| is number of instances having attribute Ai and belongs to class Ck
  • Examples:

P(Status=Married|No) = 4/7
P(Refund=Yes|Yes)=0

k

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

How to Estimate Probabilities from Data?

  • For continuous attributes:
  • Discretize the range into bins
  • one ordinal attribute per bin
  • violates independence assumption
  • Two-way split: (A < v) or (A > v)
  • choose only one of the two splits as new attribute
  • Probability density estimation:
  • Assume attribute follows a normal distribution
  • Use data to estimate parameters of distribution
    (e.g., mean and standard deviation)
  • Once probability distribution is known, can use it to estimate the conditional probability P(Ai|c)

k

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

How to Estimate Probabilities from Data?

  • Normal distribution:
  • One for each (Ai,ci) pair
  • For (Income, Class=No):
  • If Class=No
  • sample mean = 110
  • sample variance = 2975

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Example of Naïve Bayes Classifier

  • P(X|Class=No) = P(Refund=No|Class=No)
     P(Married| Class=No)
     P(Income=120K| Class=No)
    = 4/7  4/7  0.0072 = 0.0024

  • P(X|Class=Yes) = P(Refund=No| Class=Yes)
     P(Married| Class=Yes)
     P(Income=120K| Class=Yes)
    = 1  0  1.2  10-9 = 0

Since P(X|No)P(No) > P(X|Yes)P(Yes)

Therefore P(No|X) > P(Yes|X)
=> Class = No

Given a Test Record:

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Naïve Bayes Classifier

  • If one of the conditional probability is zero, then the entire expression becomes zero
  • Probability estimation:

c: number of classes

p: prior probability

m: parameter

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Example of Naïve Bayes Classifier

A: attributes

M: mammals

N: non-mammals

P(A|M)P(M) > P(A|N)P(N)

=> Mammals

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

animals2

Name Give Birth Lay Eggs Can Fly Live in Water Have Legs Class
human yes no no no yes mammals
python no yes no no no reptiles
salmon no yes no yes no fishes
whale yes no no yes no mammals
frog no yes no sometimes yes amphibians
komodo no yes no no yes reptiles
bat yes no yes no yes mammals
pigeon no yes yes no yes birds
cat yes no no no yes mammals
leopard shark yes no no yes no fishes
turtle no yes no sometimes yes reptiles
penguin no yes no sometimes yes birds
porcupine yes no no no yes mammals
eel no yes no yes no fishes
salamander no yes no sometimes yes amphibians
gila monster no yes no no yes reptiles
platypus no yes no no yes mammals
owl no yes yes no yes birds
dolphin yes no no yes no mammals
eagle no yes yes no yes birds
Name Give Birth Lay Eggs Can Fly Live in Water Have Legs Class
human yes no no no yes mammals
python no yes no no no non-mammals
salmon no yes no yes no non-mammals
whale yes no no yes no mammals
frog no yes no sometimes yes non-mammals
komodo no yes no no yes non-mammals
bat yes no yes no yes mammals
pigeon no yes yes no yes non-mammals
cat yes no no no yes mammals
leopard shark yes no no yes no non-mammals
turtle no yes no sometimes yes non-mammals
penguin no yes no sometimes yes non-mammals
porcupine yes no no no yes mammals
eel no yes no yes no non-mammals
salamander no yes no sometimes yes non-mammals
gila monster no yes no no yes non-mammals
platypus no yes no no yes mammals
owl no yes yes no yes non-mammals
dolphin yes no no yes no mammals
eagle no yes yes no yes non-mammals

animals2

Name Give Birth Lay Eggs Can Fly Live in Water Have Legs Class
human yes no no no yes mammals
python no yes no no no reptiles
salmon no yes no yes no fishes
whale yes no no yes no mammals
frog no yes no sometimes yes amphibians
komodo no yes no no yes reptiles
bat yes no yes no yes mammals
pigeon no yes yes no yes birds
cat yes no no no yes mammals
leopard shark yes no no yes no fishes
turtle no yes no sometimes yes reptiles
penguin no yes no sometimes yes birds
porcupine yes no no no yes mammals
eel no yes no yes no fishes
salamander no yes no sometimes yes amphibians
gila monster no yes no no yes reptiles
platypus no yes no no yes mammals
owl no yes yes no yes birds
dolphin yes no no yes no mammals
eagle no yes yes no yes birds
Name Give Birth Lay Eggs Can Fly Live in Water Have Legs Class
human yes no no no yes mammals
python no yes no no no non-mammals
salmon no yes no yes no non-mammals
whale yes no no yes no mammals
frog no yes no sometimes yes non-mammals
komodo no yes no no yes non-mammals
bat yes no yes no yes mammals
pigeon no yes yes no yes non-mammals
cat yes no no no yes mammals
leopard shark yes no no yes no non-mammals
turtle no yes no sometimes yes non-mammals
penguin no yes no sometimes yes non-mammals
porcupine yes no no no yes mammals
eel no yes no yes no non-mammals
salamander no yes no sometimes yes non-mammals
gila monster no yes no no yes non-mammals
platypus no yes no no yes mammals
owl no yes yes no yes non-mammals
dolphin yes no no yes no mammals
eagle no yes yes no yes non-mammals
Name Give Birth Lay Eggs Can Fly Live in Water Have Legs Class
human yes no no yes no ?

Naïve Bayes (Summary)

  • Robust to isolated noise points
  • Handle missing values by ignoring the instance during probability estimate calculations
  • Robust to irrelevant attributes
  • Independence assumption may not hold for some attributes
  • Use other techniques such as Bayesian Belief Networks (BBN)

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Artificial Neural Networks (ANN)

Output Y is 1 if at least two of the three inputs are equal to 1.

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

X1�

X2�

X3�

Y�

Black box�

Output �

Input �

Artificial Neural Networks (ANN)

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

S�

X1�

X2�

X3�

Y�

Black box�

0.3�

0.3�

0.3�

t=0.4�

Output node�

Input nodes�

Artificial Neural Networks (ANN)

  • Model is an assembly of inter-connected nodes and weighted links
  • Output node sums up each of its input value according to the weights of its links
  • Compare output node against some threshold t

Perceptron Model

or

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

S�

X1�

X2�

X3�

Y�

Black box�

w1�

w2�

w3�

t�

Output node�

Input nodes�

General Structure of ANN

Training ANN means learning the weights of the neurons

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Activation function �g(Si )�

Si�

Oi�

I1�

I2�

I3�

wi1�

wi2�

wi3�

Oi�

Neuron i�

Input�

Output�

threshold, t�

Input Layer�

Hidden Layer�

Output Layer�

x1�

x2�

x3�

x4�

x5�

y�

Algorithm for learning ANN

  • Initialize the weights (w0, w1, …, wk)
  • Adjust the weights in such a way that the output of ANN is consistent with class labels of training examples
  • Objective function:
  • Find the weights wi’s that minimize the above objective function
  • e.g., backpropagation algorithm (see lecture notes)

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Support Vector Machines

  • Find a linear hyperplane (decision boundary) that will separate the data

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Support Vector Machines

  • One Possible Solution

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

B1�

Support Vector Machines

  • Another possible solution

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

B2�

Support Vector Machines

  • Other possible solutions

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

B2�

Support Vector Machines

  • Which one is better? B1 or B2?
  • How do you define better?

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

B1�

B2�

Support Vector Machines

  • Find hyperplane maximizes the margin => B1 is better than B2

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

B1�

B2�

b11�

b12�

b21�

b22�

margin�

Support Vector Machines

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

B1�

b11�

b12�

Support Vector Machines

  • We want to maximize:
  • Which is equivalent to minimizing:
  • But subjected to the following constraints:
  • This is a constrained optimization problem

Numerical approaches to solve it (e.g., quadratic programming)

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Support Vector Machines

  • What if the problem is not linearly separable?

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Support Vector Machines

  • What if the problem is not linearly separable?
  • Introduce slack variables
  • Need to minimize:
  • Subject to:

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Nonlinear Support Vector Machines

  • What if decision boundary is not linear?

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Nonlinear Support Vector Machines

  • Transform data into higher dimensional space

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Ensemble Methods

  • Construct a set of classifiers from the training data
  • Predict class label of previously unseen records by aggregating predictions made by multiple classifiers

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

General Idea

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Original Training data�

....�

D1�

D2�

Dt-1�

Dt�

D�

Step 1: �Create Multiple Data Sets�

C1�

C2�

Ct -1�

Ct�

Step 2: �Build Multiple Classifiers�

C*�

Step 3: �Combine Classifiers�

Why does it work?

  • Suppose there are 25 base classifiers
  • Each classifier has error rate,  = 0.35
  • Assume classifiers are independent
  • Probability that the ensemble classifier makes a wrong prediction:

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Examples of Ensemble Methods

  • How to generate an ensemble of classifiers?
  • Bagging
  • Boosting

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Bagging

  • Sampling with replacement
  • Build classifier on each bootstrap sample
  • Each sample has probability (1 – 1/n)n of being selected

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Boosting

  • An iterative procedure to adaptively change distribution of training data by focusing more on previously misclassified records
  • Initially, all N records are assigned equal weights
  • Unlike bagging, weights may change at the end of boosting round

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Boosting

  • Records that are wrongly classified will have their weights increased
  • Records that are classified correctly will have their weights decreased
  • Example 4 is hard to classify
  • Its weight is increased, therefore it is more likely to be chosen again in subsequent rounds

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Example: AdaBoost

  • Base classifiers: C1, C2, …, CT

  • Error rate:

  • Importance of a classifier:

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Example: AdaBoost

  • Weight update:

  • If any intermediate rounds produce error rate higher than 50%, the weights are reverted back to 1/n and the resampling procedure is repeated
  • Classification:

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Illustrating AdaBoost

Data points for training

Initial weights for each data point

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Boosting Round 1�

+�

+�

+�

-�

-�

-�

-�

-�

-�

-�

B1�

0.0094�

0.0094�

0.4623�

a = 1.9459�

Illustrating AdaBoost

(C) Vipin Kumar, Parallel Issues in Data Mining, VECPAR 2002

Boosting Round 1�

+�

+�

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B2�

B3�

a = 1.9459�

a = 2.9323�

a = 3.8744�

YES

YES

NO

NO

NO

NO

NO

NO

Yes

No

{Married}

{Single,

Divorced}

< 80K

> 80K

Taxable

Income

Marital

Status

Refund

Classification Rules

(Refund=Yes) ==> No

(Refund=No, Marital Status={Single,Divorced},

Taxable Income<80K) ==> No

(Refund=No, Marital Status={Single,Divorced},

Taxable Income>80K) ==> Yes

(Refund=No, Marital Status={Married}) ==> No

Tid

Refund

Marital

Status

Taxable

Income

Cheat

1

Yes

Single

125K

No

2

No

Married

100K

No

3

No

Single

70K

No

4

Yes

Married

120K

No

5

No

Divorced

95K

Yes

6

No

Married

60K

No

7

Yes

Divorced

220K

No

8

No

Single

85K

Yes

9

No

Married

75K

No

10

No

Singl

e

90K

Yes

10

NameGive BirthLay EggsCan FlyLive in WaterHave LegsClass

humanyesnononoyesmammals

pythonnoyesnononoreptiles

salmonnoyesnoyesnofishes

whaleyesnonoyesnomammals

frognoyesnosometimesyesamphibians

komodonoyesnonoyesreptiles

batyesnoyesnoyesmammals

pigeonnoyesyesnoyesbirds

catyesnononoyesmammals

leopard sharkyesnonoyesnofishes

turtlenoyesnosometimesyesreptiles

penguinnoyesnosometimesyesbirds

porcupineyesnononoyesmammals

eelnoyesnoyesnofishes

salamandernoyesnosometimesyesamphibians

gila monsternoyesnonoyesreptiles

platypusnoyesnonoyesmammals

owlnoyesyesnoyesbirds

dolphinyesnonoyesnomammals

eaglenoyesyesnoyesbirds

Give

Birth?

Live In

Water?

Can

Fly?

Mammals

Fishes

Amphibians

Birds

Reptiles

Yes

No

Yes

Sometimes

No

Yes

No

Name

Blood Type

Give Birth

Can Fly

Live in Water

Class

lemur

warm

yes

no

no

?

turtle

cold

no

no

sometimes

?

dogfish shark

cold

yes

no

yes

?

Atr1

……...

AtrN

Class

A

B

B

C

A

C

B

Set of Stored Cases

k

n

n

c

+

+

=

1

(ii) Step 1

(iii) Step 2

R1

(iv) Step 3

R1

R2

PREDICTED CLASS

AmphibiansFishesReptilesBirdsMammals

ACTUALAmphibians00002

CLASSFishes03000

Reptiles00301

Birds00121

Mammals02104

PREDICTED CLASS

AmphibiansFishesReptilesBirdsMammals

ACTUALAmphibians20000

CLASSFishes02001

Reptiles10300

Birds10030

Mammals00106

Status =

Single

Status =

Divorced

Status =

Married

Income

> 80K

...

Yes: 3

No: 4

{ }

Yes: 0

No: 3

Refund=

No

Yes: 3

No: 4

Yes: 2

No: 1

Yes: 1

No: 0

Yes: 3

No: 1

(a) General-to-specific

Name

Blood Type

Give Birth

Can Fly

Live in Water

Class

turtle

cold

no

no

sometimes

?

Tid Refund Marital

Status

Taxable

Income

Class

1 Yes

Single

125K

No

2 No Married 100K

No

3 No

Single

70K

No

4 Yes Married 120K

No

5 No Divorced 95K

Yes

6 No Married 60K

No

7 Yes Divorced 220K

No

8 No

Single

85K

Yes

9 No Married 75K

No

10 No

Single

90K

Yes

10

k

n

kp

n

c

+

+

=

Name

Blood Type

Give Birth

Can Fly

Live in Water

Class

human

warm

yes

no

no

mammals

python

cold

no

no

no

reptiles

salmon

cold

no

no

yes

fishes

whale

warm

yes

no

yes

mammals

frog

cold

no

no

sometimes

amphibians

komodo

cold

no

no

no

reptiles

bat

warm

yes

yes

no

mammals

pigeon

warm

no

yes

no

birds

cat

warm

yes

no

no

mammals

leopard shark

cold

yes

no

yes

fishes

turtle

cold

no

no

sometimes

reptiles

penguin

warm

no

no

sometimes

birds

porcupine

warm

yes

no

no

mammals

eel

cold

no

no

yes

fishes

salamander

cold

no

no

sometimes

amphibians

gila monster

cold

no

no

no

reptiles

platypus

warm

no

no

no

mammals

owl

warm

no

yes

no

birds

dolphin

warm

yes

no

yes

mammals

eagle

warm

no

yes

no

birds

Name

Blood Type

Give Birth

Can Fly

Live in Water

Class

hawk

warm

no

yes

no

?

grizzly bear

warm

yes

no

no

?

Refund=No,

Status=Single,

Income=85K

(Class=Yes)

Refund=No,

Status=Single,

Income=90K

(Class=Yes)

Refund=No,

Status = Single

(Class = Yes)

(b) Specific-to-general

Rule-based Ordering

(Refund=Yes) ==> No

(Refund=No, Marital Status={Single,Divorced},

Taxable Income<80K) ==> No

(Refund=No, Marital Status={Single,Divorced},

Taxable Income>80K) ==> Yes

(Refund=No, Marital Status={Married}) ==> No

Class-based Ordering

(Refund=Yes) ==> No

(Refund=No, Marital Status={Single,Divorced},

Taxable Income<80K) ==> No

(Refund=No, Marital Status={Married}) ==> No

(Refund=No, Marital Status={Single,Divorced},

Taxable Income>80K) ==> Yes

(i) Original Data

n

n

c

=

class = +

class = -

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

-

-

-

-

--

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

+

+

+

+

+

+

+

R1

R3R2

+

+

Rule Set

r1: (P=No,Q=No) ==> -

r2: (P=No,Q=Yes) ==> +

r3: (P=Yes,R=No) ==> +

r4: (P=Yes,R=Yes,Q=No) ==> -

r5: (P=Yes,R=Yes,Q=Yes) ==> +

P

QR

Q

-++

-+

NoNo

No

Yes

Yes

Yes

NoYes

Atr1

……...

AtrN

Unseen Case

Unknown record

X

X

X

(a) 1-nearest neighbor

(b) 2-nearest neighbor

(c) 3-nearest neighbor

å

-

=

i

i

i

q

p

q

p

d

2

)

(

)

,

(

X

å

-

=

i

i

i

n

n

n

n

V

V

d

2

2

1

1

2

1

)

,

(

Tid

Refund

Marital

Status

Taxable

Income

Cheat

1

Yes

Single

125K

No

2

No

Married

100K

No

3

No

Single

70K

No

4

Yes

Married

120K

No

5

No

Divorced

95K

Yes

6

No

Married

60K

No

7

Yes

Divorced

220K

No

8

No

Single

85K

Yes

9

No

Married

75K

No

10

No

Single

90K

Yes

10

å

=

=

D

d

i

i

i

Y

X

Y

X

d

w

w

Y

X

1

2

)

,

(

)

,

(

Tid Refund Marital

Status

Taxable

Income

Cheat

X Yes Single 125K

No

Y No Married 100K

No

10

correctly

predicts

X

times

of

Number

prediction

for

used

is

X

times

of

Number

=

X

w

)

(

)

(

)

|

(

)

|

(

A

P

C

P

C

A

P

A

C

P

=

)

(

)

,

(

)

|

(

)

(

)

,

(

)

|

(

C

P

C

A

P

C

A

P

A

P

C

A

P

A

C

P

=

=

0002

.

0

20

/

1

50000

/

1

5

.

0

)

(

)

(

)

|

(

)

|

(

=

´

=

=

S

P

M

P

M

S

P

S

M

P

)

(

)

(

)

|

(

)

|

(

2

1

2

1

2

1

n

n

n

A

A

A

P

C

P

C

A

A

A

P

A

A

A

C

P

K

K

K

=

Tid

Refund

Marital

Status

Taxable

Income

Evade

1

Yes

Single

125K

No

2

No

Married

100K

No

3

No

Single

70K

No

4

Yes

Married

120K

No

5

No

Divorced

95K

Yes

6

No

Married

60K

No

7

Yes

Divorced

220K

No

8

No

Single

85K

Yes

9

No

Married

75K

No

10

No

Singl

e

90K

Yes

10

categorical

categorical

continuous

class

2

2

2

)

(

2

2

1

)

|

(

ij

ij

i

A

ij

j

i

e

c

A

P

s

m

ps

-

-

=

0072

.

0

)

54

.

54

(

2

1

)

|

120

(

)

2975

(

2

)

110

120

(

2

=

=

=

-

-

e

No

Income

P

p

P(Refund=Yes|No) = 3/7

P(Refund=No|No) = 4/7

P(Refund=Yes|Yes) = 0

P(Refund=No|Yes) = 1

P(Marital Status=Single|No) = 2/7

P(Marital Status=Divorced|No)=1/7

P(Marital Status=Married|No) = 4/7

P(Marital Status=Single|Yes) = 2/7

P(Marital Status=Divorced|Yes)=1/7

P(Marital Status=Married|Yes) = 0

For taxable income:

If class=No:

sample mean=110

sample variance=2975

If class=Yes:

sample mean=90

sample variance=25

naive Bayes Classifier:

120K)

Income

Married,

No,

Refund

(

=

=

=

X

m

N

mp

N

C

A

P

c

N

N

C

A

P

N

N

C

A

P

c

ic

i

c

ic

i

c

ic

i

+

+

=

+

+

=

=

)

|

(

:

estimate

-

m

1

)

|

(

:

Laplace

)

|

(

:

Original

NameGive BirthCan FlyLive in WaterHave LegsClass

humanyesnonoyesmammals

pythonnononononon-mammals

salmonnonoyesnonon-mammals

whaleyesnoyesnomammals

frognonosometimesyesnon-mammals

komodonononoyesnon-mammals

batyesyesnoyesmammals

pigeonnoyesnoyesnon-mammals

catyesnonoyesmammals

leopard sharkyesnoyesnonon-mammals

turtlenonosometimesyesnon-mammals

penguinnonosometimesyesnon-mammals

porcupineyesnonoyesmammals

eelnonoyesnonon-mammals

salamandernonosometimesyesnon-mammals

gila monsternononoyesnon-mammals

platypusnononoyesmammals

owlnoyesnoyesnon-mammals

dolphinyesnoyesnomammals

eaglenoyesnoyesnon-mammals

Give BirthCan FlyLive in WaterHave LegsClass

yesnoyesno?

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7

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Bagging (Round 2)

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Original Data

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0.00940.00940.4623

B1

 = 1.9459

Original

Data

+++

-----

++

0.1

0.10.1

Boosting

Round 1

+++

-------

Boosting

Round 2

--------

++

Boosting

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++++++++++

Overall

+++

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++

0.00940.00940.4623

0.3037

0.00090.0422

0.0276

0.1819

0.0038

B1

B2

B3

 = 1.9459

 = 2.9323

 = 3.8744