public override DecompositionTree Construct(Graph graph, WidthParameter widthparameter)
{
DecompositionTree tree = new DecompositionTree(graph, widthparameter);
// Create the leaves.
DecompositionNode[] nodes = new DecompositionNode[graph.Vertices.Count];
for (int i = 0; i < nodes.Length; i++)
{
tree.Nodes[i] = nodes[i] = new DecompositionNode(new BitSet(nodes.Length, graph.Vertices[i].Index), i, tree);
}
int size = nodes.Length;
while (size > 1)
{
// Find the pair of nodes whose combination is of minimal width.
double min = double.PositiveInfinity;
int first = -1, second = -1;
for (int i = 0; i < size; i++)
{
for (int j = i + 1; j < size; j++)
{
double width = widthparameter.GetWidth(graph, nodes[i].Set | nodes[j].Set);
if (width < min)
{
min = width;
first = i;
second = j;
}
}
}
// Create the parent and connect it to its children.
DecompositionNode node = new DecompositionNode(nodes[first].Set | nodes[second].Set, nodes.Length * 2 - size, tree);
tree.Attach(node, nodes[first], Branch.Left);
tree.Attach(node, nodes[second], Branch.Right);
tree.Nodes[node.Index] = node;
// Update the active set of nodes.
nodes[first] = node;
nodes[second] = nodes[size - 1];
size--;
}
tree.Attach(null, nodes[0], Branch.Left);
tree.ComputeWidth();
return(tree);
}
/// <summary>
/// Construct a linear decomposition tree from the given starting vertex.
/// </summary>
protected DecompositionTree construct(Graph graph, WidthParameter widthparameter, Vertex start)
{
DecompositionTree result = new DecompositionTree(graph, widthparameter);
int index = 0;
BitSet leftbits = new BitSet(graph.Vertices.Count, start.Index);
BitSet rightbits = ~leftbits;
BitSet neighborhood = new BitSet(start.Neighborhood);
this.add(result, start, index++);
while (!rightbits.IsEmpty)
{
Vertex selected = null;
double best = double.PositiveInfinity;
var candidates = this.candidates(graph, rightbits, leftbits, neighborhood);
foreach (var candidate in candidates)
{
BitSet left = new BitSet(leftbits);
left[candidate.Index] = true;
BitSet right = new BitSet(rightbits);
right[candidate.Index] = false;
double width = widthparameter.GetWidth(graph, left, right);
if (width < best)
{
best = width;
selected = candidate;
}
}
leftbits[selected.Index] = true;
rightbits[selected.Index] = false;
neighborhood.Or(selected.Neighborhood);
neighborhood[selected.Index] = false;
this.add(result, selected, index);
index += 2;
}
return(result);
}
