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1 function CPD = noisyor_CPD(bnet, self, leak_inhibit, inhibit)
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2 % NOISYOR_CPD Make a noisy-or CPD
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3 % CPD = NOISYOR_CPD(BNET, NODE_NUM, LEAK_INHIBIT, INHIBIT)
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4 %
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5 % A noisy-or node turns on if any of its parents are on, provided they are not inhibited.
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6 % The prob. that the i'th parent gets inhibited (flipped from 1 to 0) is inhibit(i).
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7 % The prob that the leak node (a dummy parent that is always on) gets inhibit is leak_inhibit.
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8 % These params default to random values if omitted.
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9 %
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10 % Example: suppose C has parents A and B, and the
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11 % link of A->C fails with prob pA and the link B->C fails with pB.
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12 % Then the noisy-OR gate defines the following distribution
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13 %
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14 % A B P(C=0)
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15 % 0 0 1.0
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16 % 1 0 pA
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17 % 0 1 pB
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18 % 1 1 pA * PB
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19 %
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20 % Currently, learning is not supported for noisy-or nodes
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21 % (since the M step is somewhat complicated).
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22 %
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23 % For simple generalizations of the noisy-OR model, see e.g.,
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24 % - Srinivas, "A generalization of the noisy-OR model", UAI 93
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25 % - Meek and Heckerman, "Learning Causal interaction models", UAI 97.
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26
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27
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28
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29 if nargin==0
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30 % This occurs if we are trying to load an object from a file.
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31 CPD = init_fields;
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32 CPD = class(CPD, 'noisyor_CPD', discrete_CPD(1, []));
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33 return;
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34 elseif isa(bnet, 'noisyor_CPD')
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35 % This might occur if we are copying an object.
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36 CPD = bnet;
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37 return;
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38 end
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39 CPD = init_fields;
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40
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41
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42 ps = parents(bnet.dag, self);
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43 fam = [ps self];
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44 ns = bnet.node_sizes;
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45 assert(all(ns(fam)==2));
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46 assert(isempty(myintersect(fam, bnet.cnodes)));
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47
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48 if nargin < 3, leak_inhibit = rand(1, 1); end
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49 if nargin < 4, inhibit = rand(1, length(ps)); end
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50
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51 CPD.self = self;
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52 CPD.inhibit = inhibit;
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53 CPD.leak_inhibit = leak_inhibit;
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54
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55
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56 % For BIC
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57 CPD.nparams = 0;
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58 CPD.nsamples = 0;
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59
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60 CPD.CPT = []; % cached copy, to speed up CPD_to_CPT
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61
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62 clamped = 1;
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63 CPD = class(CPD, 'noisyor_CPD', discrete_CPD(clamped, ns([ps self])));
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64
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65
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66
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67 %%%%%%%%%%%
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68
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69 function CPD = init_fields()
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70 % This ensures we define the fields in the same order
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71 % no matter whether we load an object from a file,
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72 % or create it from scratch. (Matlab requires this.)
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73
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74 CPD.self = [];
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75 CPD.inhibit = [];
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76 CPD.leak_inhibit = [];
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77 CPD.nparams = [];
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78 CPD.nsamples = [];
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79 CPD.CPT = [];
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