Miscellaneous smaller improvements
[libdai.git] / src / clustergraph.cpp
1 /* This file is part of libDAI - http://www.libdai.org/
2 *
3 * libDAI is licensed under the terms of the GNU General Public License version
4 * 2, or (at your option) any later version. libDAI is distributed without any
5 * warranty. See the file COPYING for more details.
6 *
7 * Copyright (C) 2006-2009 Joris Mooij [joris dot mooij at libdai dot org]
8 * Copyright (C) 2006-2007 Radboud University Nijmegen, The Netherlands
9 */
10
11
12 #include <set>
13 #include <vector>
14 #include <iostream>
15 #include <dai/varset.h>
16 #include <dai/clustergraph.h>
17
18
19 namespace dai {
20
21
22 using namespace std;
23
24
25 ClusterGraph::ClusterGraph( const std::vector<VarSet> & cls ) : G(), vars(), clusters() {
26 // construct vars, clusters and edge list
27 vector<Edge> edges;
28 foreach( const VarSet &cl, cls ) {
29 if( find( clusters.begin(), clusters.end(), cl ) == clusters.end() ) {
30 // add cluster
31 size_t n2 = clusters.size();
32 clusters.push_back( cl );
33 for( VarSet::const_iterator n = cl.begin(); n != cl.end(); n++ ) {
34 size_t n1 = find( vars.begin(), vars.end(), *n ) - vars.begin();
35 if( n1 == vars.size() )
36 // add variable
37 vars.push_back( *n );
38 edges.push_back( Edge( n1, n2 ) );
39 }
40 } // disregard duplicate clusters
41 }
42
43 // Create bipartite graph
44 G.construct( vars.size(), clusters.size(), edges.begin(), edges.end() );
45 }
46
47
48
49 ClusterGraph ClusterGraph::VarElim( const std::vector<Var> &ElimSeq ) const {
50 // Make a copy
51 ClusterGraph cl(*this);
52 cl.eraseNonMaximal();
53
54 ClusterGraph result;
55
56 // Do variable elimination
57 for( vector<Var>::const_iterator n = ElimSeq.begin(); n != ElimSeq.end(); n++ ) {
58 size_t i = cl.findVar( *n );
59 DAI_ASSERT( i != cl.vars.size() );
60
61 result.insert( cl.Delta(i) );
62
63 cl.insert( cl.delta(i) );
64 cl.eraseSubsuming( i );
65 cl.eraseNonMaximal();
66 }
67
68 return result;
69 }
70
71
72 size_t eliminationCost_MinFill( const ClusterGraph &cl, size_t i ) {
73 std::vector<size_t> id_n = cl.G.delta1( i );
74
75 size_t cost = 0;
76
77 // for each unordered pair {i1,i2} adjacent to n
78 for( size_t _i1 = 0; _i1 < id_n.size(); _i1++ )
79 for( size_t _i2 = _i1 + 1; _i2 < id_n.size(); _i2++ ) {
80 // if i1 and i2 are not adjacent, eliminating n would make them adjacent
81 if( !cl.adj(id_n[_i1], id_n[_i2]) )
82 cost++;
83 }
84
85 return cost;
86 }
87
88
89 size_t eliminationChoice_MinFill( const ClusterGraph &cl, const std::set<size_t> &remainingVars ) {
90 set<size_t>::const_iterator lowest = remainingVars.end();
91 size_t lowest_cost = -1UL;
92 for( set<size_t>::const_iterator i = remainingVars.begin(); i != remainingVars.end(); i++ ) {
93 size_t cost = eliminationCost_MinFill( cl, *i );
94 if( lowest == remainingVars.end() || lowest_cost > cost ) {
95 lowest = i;
96 lowest_cost = cost;
97 }
98 }
99 return *lowest;
100 }
101
102
103 } // end of namespace dai