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1 function seq = sample_dbn(bnet, varargin)
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2 % SAMPLE_DBN Generate a random sequence from a DBN.
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3 % seq = sample_dbn(bnet, ...)
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4 %
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5 % seq{i,t} contains the values of the i'th node in the t'th slice.
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6 %
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7 % Optional arguments:
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8 %
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9 % length - length of sequence to be generated (can also just use sample_dbn(bnet,T))
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10 % stop_test - name of a function which is used to decide when to stop;
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11 % This will be called as feval(stop_test, seq(:,t))
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12 % i.e., stop_test is passed a cell array containing all the nodes in the current slice.
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13 % evidence - initial evidence; if evidence{i,t} is non-empty, this node won't be sampled.
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14
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15 args = varargin;
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16 nargs = length(args);
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17
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18 if (nargs == 1) & ~isstr(args{1})
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19 % Old syntax: sample_dbn(bnet, T)
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20 T = args{1};
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21 else
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22 % get length
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23 T = 1;
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24 for i=1:2:nargs
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25 switch args{i},
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26 case 'length', T = args{i+1};
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27 case 'evidence', T = size(args{i+1}, 2);
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28 end
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29 end
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30 end
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31
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32 ss = length(bnet.intra);
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33 % set default arguments
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34 seq = cell(ss, T);
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35 stop_test = [];
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36 for i=1:2:nargs
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37 switch args{i},
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38 case 'evidence', seq = args{i+1}; % initialise observed nodes
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39 case 'stop_test', stop_test = args{i+1};
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40 end
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41 end
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42
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43 t = 1;
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44 for i=1:ss
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45 if ~isempty(stop_test) | isempty(seq{i,t})
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46 ps = parents(bnet.dag, i);
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47 e = bnet.equiv_class(i,1);
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48 pvals = seq(ps);
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49 seq{i,t} = sample_node(bnet.CPD{e}, pvals);
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50 %fprintf('sample i=%d,t=%d,val=%d,ps\n', i, t, seq(i,t)); pvals(:)'
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51 end
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52 end
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53 t = 2;
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54 done = 0;
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55 while ~done
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56 for i=1:ss
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57 if ~isempty(stop_test) | isempty(seq{i,t})
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58 ps = parents(bnet.dag, i+ss) + (t-2)*ss;
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59 e = bnet.equiv_class(i,2);
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60 pvals = seq(ps);
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61 seq{i,t} = sample_node(bnet.CPD{e}, pvals);
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62 %fprintf('sample i=%d,t=%d,val=%d,ps\n', i, t, seq(i,t)); pvals(:)'
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63 end
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64 end
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65 if ~isempty(stop_test)
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66 done = feval(stop_test, seq(:,t));
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67 else
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68 if t==T
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69 done = 1;
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70 end
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71 end
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72 t = t + 1;
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73 end
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