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1 function slice = get_slice_dbn(bnet, state, i, n, j, m, strides, families, ...
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2 CPT)
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3 % slice = get_slice(bnet, state, i, n, j, m, strides, families, cpt)
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4 %
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5 % GET_SLICE get one-dimensional slice of the CPT for node X_i^n
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6 % that corresponds to the different values of X_j^m, where all
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7 % other nodes have values given by state.
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8 % strides is the result of
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9 % calling compute_strides(bnet)
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10 % families is the result of calling compute_families(bnet)
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11 % cpts is the result of calling get_cpts(bnet)
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12 %
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13 % slice is a 1-d array
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14
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15
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16 if (n == 1)
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17
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18 k = bnet.eclass1(i);
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19 c = CPT{k};
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20
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21 % Figure out evidence on family
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22 fam = families{i, 1};
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23 ev = state(fam, 1);
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24
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25 % Remove evidence on node j
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26 pos = find(fam == j);
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27 ev(pos) = 1;
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28 dim = size(ev, 1);
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29
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30 % Compute initial index and stride
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31 start_ind = 1+strides(k, 1:dim)*(ev-1);
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32 stride = strides(k, pos);
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33
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34 % Compute the slice
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35 slice = c(start_ind:stride:start_ind+(bnet.node_sizes(j, 1)-1)*stride);
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36
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37 else
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38
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39 k = bnet.eclass2(i);
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40 c = CPT{k};
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41
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42 fam = families{i, 2};
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43 ss = length(bnet.intra);
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44
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45 % Divide the family into nodes in this time step and nodes in the
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46 % previous time step
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47 this_time_step = fam(find(fam > ss));
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48 prev_time_step = fam(find(fam <= ss));
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49
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50 % Normalize the node numbers
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51 this_time_step = this_time_step - ss;
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52
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53 % Get the evidence
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54 this_step_ev = state(this_time_step, n);
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55 prev_step_ev = state(prev_time_step, n-1);
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56
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57 % Remove the evidence for X_j^m
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58 if (m == n)
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59 pos = find(this_time_step == j);
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60 this_step_ev(pos) = 1;
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61 pos = pos + size(prev_time_step, 2);
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62 else
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63 assert (m == n-1);
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64 pos = find(prev_time_step == j);
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65 prev_step_ev(pos) = 1;
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66 end
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67
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68 % Combine the two time steps
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69 ev = [prev_step_ev; this_step_ev];
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70 dim = size(ev, 1);
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71
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72
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73 % Compute starting index and stride
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74 start_ind = 1 + strides(k, 1:dim)*(ev-1);
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75 stride = strides(k, pos);
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76
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77 % Compute slice
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78 if (m == 1)
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79 q = 1;
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80 else
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81 q = 2;
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82 end
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83 slice = c(start_ind:stride:start_ind+(bnet.node_sizes(j, q)-1)*stride);
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84 end
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85
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86
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87
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