private boolean nodesCanBeMapped(
IsomorphismCalculator rhs,
Map<Integer, Integer> mapping,
Set<Integer> mappedLhsNodes,
Set<Integer> mappedRhsNodes,
Set<Integer> leadingEdgeNodes) {
assert mapping.size() == mappedLhsNodes.size() && mapping.size() == mappedRhsNodes.size()
: String.format(
"Mapping sizes are different: %s, %s, %s",
mapping.size(), mappedLhsNodes.size(), mappedRhsNodes.size());
assert mappingInvariantsSatisfied() : "Bug detected. Should never happen";
if (mapping.size() == size) return true;
Integer node = chooseNode(mappedLhsNodes, leadingEdgeNodes);
mappedLhsNodes.add(node);
Set<Integer> newLeadingEdgeNodes = new HashSet<Integer>(leadingEdgeNodes);
newLeadingEdgeNodes.addAll(qecGraph.neighbours(node));
newLeadingEdgeNodes.removeAll(mappedLhsNodes);
Iterable<Integer> rhsCandidates = findCandidateMappings(node, rhs, mapping, mappedRhsNodes);
for (Integer rhsNode : rhsCandidates) {
mapping.put(node, rhsNode);
mappedRhsNodes.add(rhsNode);
if (nodesCanBeMapped(rhs, mapping, mappedLhsNodes, mappedRhsNodes, newLeadingEdgeNodes)) {
assert mappingInvariantsSatisfied() : "Bug detected. Should never happen";
return true;
}
mapping.remove(node);
mappedRhsNodes.remove(rhsNode);
}
mappedLhsNodes.remove(node);
assert mappingInvariantsSatisfied() : "Bug detected. Should never happen";
return false;
}
private Map<NodeCharacterisation, Set<Integer>> createCharacterisationMappings() {
Map<NodeCharacterisation, Set<Integer>> mapping =
new HashMap<NodeCharacterisation, Set<Integer>>();
for (int node = 0; node < size; node++) {
int blackNeighbourCount = 0;
int whiteNeighbourCount = 0;
for (int possibleNeighbour = 0; possibleNeighbour < size; possibleNeighbour++) {
if (qecGraph.edge(node, possibleNeighbour)) {
if (qecGraph.isBlack(possibleNeighbour)) {
blackNeighbourCount++;
} else {
whiteNeighbourCount++;
}
}
}
addToCharacterisationMappings(
mapping, node, qecGraph.isBlack(node), blackNeighbourCount, whiteNeighbourCount);
}
return mapping;
}
private Set<Integer> filterAgainstExistingMappings(
Integer node,
IsomorphismCalculator rhs,
Map<Integer, Integer> mapping,
Set<Integer> candidateMappings) {
Collection<Integer> neighbours = qecGraph.neighbours(node);
Set<Integer> filteredCandidates = new HashSet<Integer>();
for (Integer candidate : candidateMappings) {
if (agreesWithExistingMappings(candidate, neighbours, rhs, mapping)) {
filteredCandidates.add(candidate);
}
}
return filteredCandidates;
}
private int getNumberOfBlackNodes() {
if (numberOfBlackNodes < 0) numberOfBlackNodes = qecGraph.getNumberOfBlackNodes();
return numberOfBlackNodes;
}
public IsomorphismCalculator(QecGraph qecGraph) {
this.qecGraph = qecGraph;
size = qecGraph.getSize();
}