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A. Darwiche Bayesian Networks. A. Darwiche Reasoning Systems Diagnostics: Which component failed? Information retrieval: What document to retrieve? On-line.

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Presentation on theme: "A. Darwiche Bayesian Networks. A. Darwiche Reasoning Systems Diagnostics: Which component failed? Information retrieval: What document to retrieve? On-line."— Presentation transcript:

1 A. Darwiche Bayesian Networks

2 A. Darwiche Reasoning Systems Diagnostics: Which component failed? Information retrieval: What document to retrieve? On-line help: What is he trying to do? E-commerce: Is he interested in books? CAD: Does the design meet the specification? Decoders: What was the original message? Predictive maintenance: Will the device break?

3 A. Darwiche Model-Based Reasoning Formal Model (KB) Reasoning Engine Query Conclusions What modeling language? How to get the model? How to reason efficiently?

4 A. Darwiche Bayesian Network Battery Age Alternator Fan Belt Battery Charge Delivered Battery Power Starter Radio LightsEngine Turn Over Gas Gauge Gas Fuel Pump Fuel Line Distributor Spark Plugs Engine Start

5 A. Darwiche Bayesian Network Battery Age Alternator Fan Belt Battery Charge Delivered Battery Power Starter Radio LightsEngine Turn Over Gas Gauge Gas Fuel Pump Fuel Line Distributor Spark Plugs Engine Start Pr(Lights=ON | Battery-Power=OK) =.99 ON OFF OK WEAK DEAD Lights Battery Power θ 1 + θ 2 = 1

6 A. Darwiche Model-Based Reasoning Efficiency: Time and space resources (algorithms) Formalization –What modeling language? (symbolic, quantitative) –What query semantics? (diagnosis, recommender, belief revision, causality) Synthesis of models –Knowledge engineering (sensitivity analysis) –Synthesize from design information (model checking, verfication) –Synthesize from online data (learning) Embeddability (compiled reasoning, anyspace reasoning)

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11 Diagnosis Scenario Battery Age Alternator Fan Belt Battery Charge Delivered Battery Power Starter Radio LightsEngine Turn Over Gas Gauge Gas Fuel Pump Fuel Line Distributor Spark Plugs Engine Start Query Behavior

12 A. Darwiche Diagnosis Scenario Battery Age Alternator Fan Belt Battery Charge Delivered Battery Power Starter Radio LightsEngine Turn Over Gas Gauge Gas Fuel Pump Fuel Line Distributor Spark Plugs Engine Start okonyesno.001 okoffyesno.090

13 A. Darwiche Probabilistic Reasoning Battery Age Alternator Fan Belt Battery Charge Delivered Battery Power Starter Radio LightsEngine Turn Over Gas Gauge Gas Fuel Pump Fuel Line Distributor Spark Plugs Engine Start Posterior Marginals

14 A. Darwiche Probabilistic Reasoning Battery Age Alternator Fan Belt Battery Charge Delivered Battery Power Starter Radio LightsEngine Turn Over Gas Gauge Gas Fuel Pump Fuel Line Distributor Spark Plugs Engine Start Maximum a Posteriori (MAP)

15 A. Darwiche Probabilistic Reasoning Battery Age Alternator Fan Belt Battery Charge Delivered Battery Power Starter Radio LightsEngine Turn Over Gas Gauge Gas Fuel Pump Fuel Line Distributor Spark Plugs Engine Start Maximum a Posteriori (MAP)

16 A. Darwiche Probabilistic Reasoning Battery Age Alternator Fan Belt Battery Charge Delivered Battery Power Starter Radio LightsEngine Turn Over Gas Gauge Gas Fuel Pump Fuel Line Distributor Spark Plugs Engine Start Maximum a Posteriori (MAP)

17 A. Darwiche Probabilistic Reasoning Battery Age Alternator Fan Belt Battery Charge Delivered Battery Power Starter Radio LightsEngine Turn Over Gas Gauge Gas Fuel Pump Fuel Line Distributor Spark Plugs Engine Start Maximum a Posteriori (MAP)

18 A. Darwiche Diagnostic System Battery Age Alternator Fan Belt Battery Charge Delivered Battery Power Starter Radio LightsEngine Turn Over Gas Gauge Gas Fuel Pump Fuel Line Distributor Spark Plugs Engine Start Bayesian Network Inference Engine okonyesno okoffyesno

19 A. Darwiche Agenda Propositional (Boolean) Logic Probability Calculus Independence & Causality Bayesian networks: –Markovian Assumption –Chain Rule for Bayesian Networks –d-separation

20 A. Darwiche Propositional Logic

21 A. Darwiche Probablity Calculus

22 A. Darwiche Bayesian Networks

23 A. Darwiche A Bayesian Network Compact representation of a probability distribution: –Complete model –Consistent model Embeds many independence assumptions: –Faithful model

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28 A Bayesian Network Compact representation of a probability distribution: –Complete model –Consistent model Embeds many independence assumptions: –Faithful model

29 A. Darwiche Bayesian Network Earthquake (E) Burglary (B) Alarm (A) Pr(E=true)Pr(E=false).1.9 Pr(B=true)Pr(B=false).2.8 Pr(A=true)Pr(A=false) E=true, B=true E=false, B=true.9.1 E=true, B=false.7.3 E=false, B=false.01.99

30 A. Darwiche Joint Probability Distribution EBAPr(.) True.019 True False.001 TrueFalseTrue.056 TrueFalse.024 FalseTrue.162 FalseTrueFalse.018 False True.0072 False.7128

31 A. Darwiche Independence Assumptions of a Bayesian Network

32 A. Darwiche Chol Test1Test2 Causal Structure I(Test1,Test2 | Chol)

33 A. Darwiche Chol Test1Test2 Causal Structure Nurse I(Test1,Test2 | Chol, Nurse) I(Test1,Test2 | Chol)

34 A. Darwiche H O1On Naïve Bayes O2 H: Disease O1, …, On: Findings (symptoms, lab tests, …) …

35 A. Darwiche Genetic Tracking G1G2 G3G4G5 G6 G7G8P4 Each node is independent of its non-descendants given its parents

36 A. Darwiche Genetic Tracking G1G2 G3G4G5 G6 G7G8P4 Each node is independent of its non-descendants given its parents

37 A. Darwiche Genetic Tracking G1G2 G3G4G5 G6 G7G8P4 Each node is independent of its non-descendants given its parents

38 A. Darwiche Dynamic Systems S1 O1 S2 O2 S3 O3 S4 O4 S5 O5 Each node is independent of its non-descendants given its parents

39 A. Darwiche Dynamic Systems S1 O1 S2 O2 S3 O3 S4 O4 S5 O5 Each node is independent of its non-descendants given its parents

40 A. Darwiche The chain rule for Bayesian Networks

41 A. Darwiche Earthquake (E) Burglary (B) Alarm (A) Call (C) Radio (R) Pr(c|a) Pr(craeb)=Pr(c|raeb)Pr(r|aeb)Pr(a|eb)Pr(e|b)Pr(b) Pr(r|e)Pr(a|eb)Pr(e)Pr(b) Pr(e)Pr(b) Pr(a|eb) Pr(r|e) Pr(c|a)

42 A. Darwiche Example: Build Joint Probability Table Earthquake (E) Burglary (B) Alarm (A) Pr(E=true)Pr(E=false).1.9 Pr(B=true)Pr(B=false).2.8 Pr(A=true)Pr(A=false) E=true, B=true E=false, B=true.9.1 E=true, B=false.7.3 E=false, B=false.01.99

43 A. Darwiche Temperature/Sensors Temperature: high (20%), low (10%), nominal (70%) 3 Sensors (true, false): true (90%) given high temperature true (1%) given low temperature true (5%) given nominal temperature

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47 Queries Pr(Sensor1=true)? Pr(Temperature=high | Sensor1=true)? Pr(Temperature=high | Sensor1=true, Sensor2=true, Sensor3=true)?

48 A. Darwiche d-separation

49 Earthquake (E) Burglary (B) Alarm (A) Call (C) Radio (R) … (F) Is A Independent of R given E?

50 A. Darwiche Earthquake (E) Burglary (B) Alarm (A) Call (C) Radio (R) Chain Link E & C not d-separated …Active!

51 A. Darwiche Earthquake (E) Burglary (B) Alarm (A) Call (C) Radio (R) Chain Link E & C are d-separated by A …Blocked!

52 A. Darwiche Earthquake (E) Burglary (B) Alarm (A) Call (C) Radio (R) Divergent Link R & A not d-seperated …Active!

53 A. Darwiche Earthquake (E) Burglary (B) Alarm (A) Call (C) Radio (R) Divergent Link R & A d-separated by E …Blocked!

54 A. Darwiche Earthquake (E) Burglary (B) Alarm (A) Call (C) Radio (R) Convergent Link E & B d-seperated …Blocked!

55 A. Darwiche Earthquake (E) Burglary (B) Alarm (A) Call (C) Radio (R) Convergent Link E & B not d-separated by A …Active!

56 A. Darwiche Earthquake (E) Burglary (B) Alarm (A) Call (C) Radio (R) Convergent Link E & B not d-separated by C …Active!

57 A. Darwiche Earthquake (E) Burglary (B) Alarm (A) Call (C) Radio (R) Are B & R d-separated by E & C ? Active Blocked

58 A. Darwiche Earthquake (E) Burglary (B) Alarm (A) Call (C) Radio (R) Active Are C & R d-separated ?

59 A. Darwiche blocked active

60 A. Darwiche d-separation Nodes X are d-separated from nodes Y by nodes Z iff every path from X to Y is blocked by Z. A path is blocked by Z if some link on the path is blocked: –For some →X→ or ←X→, X in Z –For some →X←, neither X nor one of its descendents in Z

61 A. Darwiche d-separation in Asia Network Visit to Asia / Smoker: –No evidence: No –Given TB-or-Cancer: Yes –Given +ve X-Ray: Yes Visit to Asia / +ve X-ray: –No evidence: Yes –Given TB: No –Given TB-or-Cancer: No Bronchitis / Lung Cancer: –No evidence: Yes –Given Smoker: No –Given Smoker and Dysnpnoea: Yes

62 A. Darwiche Building Bayesian Networks

63 A. Darwiche Three Steps Identifying variables Catching the structure Defining the CPTs

64 A. Darwiche Identifying Variables Hypothesis variables Information variables (observables) Others (mediate relationships)

65 A. Darwiche Car Start Problem “In the morning, my car will not start. I can hear the starter turn, but nothing happens. There May be several reasons for my problem. I can hear the starter roll, so there must be power in the battery. Therefore, the most probable causes are that the fuel has been stolen overnight or that the spark plugs are dirty. It may also be due to dirt in the carburetor, a leak in the ignition system, or something more serious. To find out, I first look at the fuel meter. It shows ½ full, so I decide to clean the spark plugs”

66 A. Darwiche Car Start Problem “In the morning, my car will not start. I can hear the starter turn, but nothing happens. There May be several reasons for my problem. I can hear the starter roll, so there must be power in the battery. Therefore, the most probable causes are that the fuel has been stolen overnight or that the spark plugs are dirty. It may also be due to dirt in the carburetor, a leak in the ignition system, or something more serious. To find out, I first look at the fuel meter. It shows ½ full, so I decide to clean the spark plugs” Fuel Meter Standing Fuel? Start? Clean Spark Plugs

67 A. Darwiche Fuel Meter Standing “FM” Fuel? “Fu” Start? “St” Clean Spark Plugs “Sp” Fu = yes Fu = no FM = full FM = ½ FM = empty Fu = yes Fu = no Sp = yes (0.99, 0.01) (0,1) Sp = no (0.01, 0.99) (0,1) P(FM | Fu) P(St | Fu,Sp)

68 A. Darwiche Milk test “Milk from a cow may be infected. To detect whether the milk is infected, you have a test, which may give either a positive or a negative test result. The test is not perfect. It may give a positive result on a clean milk as well as a negative result on infected milk” Infected?Test

69 A. Darwiche Digital Systems...

70 A. Darwiche Digital Systems Build network structure Specificy CPTs Fault modes What if we have two test vectors Single vs multiple faults How to pose queries Synthesis automatically

71 A. Darwiche Channel Coding Information bits: U 1 … U k Redundant bits: X 1 …X m Code word: U 1 …U k X 1 … X m (Channel input) Channel output: Y 1 …Y k+m Given channel output Y, restore the channel input

72 A. Darwiche Channel Coding U1 U2 U4 Y1 Y2 Y3 Y4 Y5 Y6Y7 X1 X2 X3 U3 (7,4) Hamming code

73 A. Darwiche Noisy-Or

74 E C1C1 C2C2 CnCn... LNoisy-OR CnCn C2C2 C1C1 L E Global enabler (leak) 1

75 A. Darwiche Let v be an assignment of truth values to C1…Cn Let S contain all indices i such that Ci=true E... CnCn C2C2 C1C1 L Global enabler (leak) 1

76 A. Darwiche O(n) parameters instead of O(2 n ) CPCS network : 448 nodes 906 links 8254 parameters; instead of 134 million! Noisy-OR

77 A. DarwicheNoisy-Or 5% of the mornings yields a sore throat (l =.95) Cold causes a sore throat with probability 0.4; (q=.6) Angina causes a sore throat with probability 0.7 (q=.3) Cold? SoreThroat? Angina?

78 A. DarwicheNoisy-Or Cold? SoreThroat? Angina? Angina? = noAngina? = yes Cold? = no * 0.3 Cold? = yes0.95 * * 0.3 * 0.6 P(SoreThroat? = no | Cold?, Angina? )

79 A. DarwicheNoisy-Or Angina? = noAngina? = yes Cold? = no * 0.3 Cold? = yes * * 0.3 * 0.6 P(SoreThroat? = yes | Cold?, Angina? ) Cold? SoreThroat? Angina?


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