comparison toolboxes/FullBNT-1.0.7/bnt/general/determine_elim_constraints.m @ 0:e9a9cd732c1e tip

first hg version after svn
author wolffd
date Tue, 10 Feb 2015 15:05:51 +0000
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1 function partial_order = determine_elim_constraints(bnet, onodes)
2 % DETERMINE_ELIM_CONSTRAINTS Determine what the constraints are (if any) on the elimination ordering.
3 % partial_order = determine_elim_constraints(bnet, onodes)
4 %
5 % A graph with different kinds of nodes (e.g., discrete and cts, or decision and rnd) is called marked.
6 % A strong root is guaranteed to exist if the marked graph is triangulated and does not have any paths of
7 % the form discrete -> cts -> discrete. In general we need to add extra edges to
8 % the moral graph to ensure this (see example in Lauritzen (1992) fig 3b).
9 % However, a simpler sufficient condition is to eliminate all the cts nodes before the discrete ones,
10 % because then, as we move from the leaves to the root, the cts nodes get marginalized away
11 % and we are left with purely discrete cliques.
12 %
13 % partial_order(i,j)=1 if we must marginalize j *before* i
14 % (so i will be nearer the strong root).
15 % If the hidden nodes are either all discrete or all cts, we set partial_order = [].
16 %
17 % For details, see
18 % - Jensen, Jensen and Dittmer, "From influence diagrams to junction trees", UAI 94.
19 % - Lauritzen, "Propgation of probabilities, means, and variances in mixed graphical
20 % association models", JASA 87(420):1098--1108, 1992.
21 % - K. Olesen, "Causal probabilistic networks with both discrete and continuous variables",
22 % IEEE Pami 15(3), 1993
23
24
25 n = length(bnet.dag);
26 pot_type = determine_pot_type(bnet, onodes);
27 if (pot_type == 'd') | (pot_type == 'g')
28 partial_order = [];
29 return;
30 end
31
32
33 partial_order = sparse(n,n);
34 partial_order(bnet.dnodes, bnet.cnodes) = 1;
35
36 % Integrate out cts nodes before their discrete parents - see Olesen (1993) p9
37 % This method gives the wrong results on cg1.m!
38 if 0
39 for i=bnet.cnodes(:)'
40 dps = myintersect(parents(bnet.dag, i), bnet.dnodes);
41 partial_order(dps, i)=1;
42 end
43 end