package edu.stanford.nlp.fsm;
import edu.stanford.nlp.trees.PennTreebankLanguagePack;
import edu.stanford.nlp.util.Maps;
import java.util.*;
/**
* Minimization in n log n a la Hopcroft.
*
* @author Dan Klein (klein@cs.stanford.edu)
*/
public class FastExactAutomatonMinimizer implements AutomatonMinimizer {
TransducerGraph unminimizedFA = null;
Map memberToBlock = null;
LinkedList splits = null;
boolean sparseMode = true;
static final Object SINK_NODE = "SINK_NODE";
static class Split {
Collection members;
Object symbol;
Block block;
public Collection getMembers() {
return members;
}
public Object getSymbol() {
return symbol;
}
public Block getBlock() {
return block;
}
public Split(Collection members, Object symbol, Block block) {
this.members = members;
this.symbol = symbol;
this.block = block;
}
}
static class Block {
Set members;
public Set getMembers() {
return members;
}
public Block(Set members) {
this.members = members;
}
}
protected TransducerGraph getUnminimizedFA() {
return unminimizedFA;
}
protected Collection getSymbols() {
return getUnminimizedFA().getInputs();
}
public TransducerGraph minimizeFA(TransducerGraph unminimizedFA) {
// System.out.println(unminimizedFA);
this.unminimizedFA = unminimizedFA;
this.splits = new LinkedList();
this.memberToBlock = new HashMap(); //new IdentityHashMap(); // TEG: I had to change this b/c some weren't matching
minimize();
return buildMinimizedFA();
}
protected TransducerGraph buildMinimizedFA() {
TransducerGraph minimizedFA = new TransducerGraph();
TransducerGraph unminimizedFA = getUnminimizedFA();
for (TransducerGraph.Arc arc : unminimizedFA.getArcs()) {
Object source = projectNode(arc.getSourceNode());
Object target = projectNode(arc.getTargetNode());
try {
if (minimizedFA.canAddArc(source, target, arc.getInput(), arc.getOutput())) {
minimizedFA.addArc(source, target, arc.getInput(), arc.getOutput());
}
} catch (Exception e) {
//throw new IllegalArgumentException();
}
}
minimizedFA.setStartNode(projectNode(unminimizedFA.getStartNode()));
for (Object o : unminimizedFA.getEndNodes()) {
minimizedFA.setEndNode(projectNode(o));
}
return minimizedFA;
}
protected Object projectNode(Object node) {
Set members = getBlock(node).getMembers();
return members;
}
protected boolean hasSplit() {
return splits.size() > 0;
}
protected Split getSplit() {
return (Split) splits.removeFirst();
}
protected void addSplit(Split split) {
splits.addLast(split);
}
// protected Collection inverseImages(Collection block, Object symbol) {
// List inverseImages = new ArrayList();
// for (Iterator nodeI = block.iterator(); nodeI.hasNext();) {
// Object node = nodeI.next();
// inverseImages.addAll(getUnminimizedFA().getInboundArcs(node, symbol));
// }
// return inverseImages;
// }
protected Map sortIntoBlocks(Collection nodes) {
Map blockToMembers = new IdentityHashMap();
for (Object o : nodes) {
Block block = getBlock(o);
Maps.putIntoValueHashSet(blockToMembers, block, o);
}
return blockToMembers;
}
protected void makeBlock(Collection members) {
Block block = new Block(new HashSet(members));
for (Object member : block.getMembers()) {
if (member != SINK_NODE) {
// System.out.println("putting in memberToBlock: " + member + " " + block);
memberToBlock.put(member, block);
}
}
addSplits(block);
}
protected void addSplits(Block block) {
Map symbolToTarget = new HashMap();
for (Object member : block.getMembers()) {
for (Object o : getInverseArcs(member)) {
TransducerGraph.Arc arc = (TransducerGraph.Arc) o;
Object symbol = arc.getInput();
Object target = arc.getTargetNode();
Maps.putIntoValueArrayList(symbolToTarget, symbol, target);
}
}
for (Object symbol : symbolToTarget.keySet()) {
addSplit(new Split((List) symbolToTarget.get(symbol), symbol, block));
}
}
protected void removeAll(Collection block, Collection members) {
// this is because AbstractCollection/Set.removeAll() isn't always linear in members.size()
for (Object member : members) {
block.remove(member);
}
}
protected Collection difference(Collection block, Collection members) {
Set difference = new HashSet();
for (Object member : block) {
if (!members.contains(member)) {
difference.add(member);
}
}
return difference;
}
protected Block getBlock(Object o) {
Block result = (Block) memberToBlock.get(o);
if (result == null) {
System.out.println("No block found for: " + o); // debug
System.out.println("But I do have blocks for: ");
for (Object o1 : memberToBlock.keySet()) {
System.out.println(o1);
}
throw new RuntimeException("FastExactAutomatonMinimizer: no block found");
}
return result;
}
protected Collection getInverseImages(Split split) {
List inverseImages = new ArrayList();
Object symbol = split.getSymbol();
Block block = split.getBlock();
for (Object member : split.getMembers()) {
if (!block.getMembers().contains(member)) {
continue;
}
Collection arcs = getInverseArcs(member, symbol);
for (Object arc1 : arcs) {
TransducerGraph.Arc arc = (TransducerGraph.Arc) arc1;
Object source = arc.getSourceNode();
inverseImages.add(source);
}
}
return inverseImages;
}
protected Collection getInverseArcs(Object member, Object symbol) {
if (member != SINK_NODE) {
return getUnminimizedFA().getArcsByTargetAndInput(member, symbol);
}
return getUnminimizedFA().getArcsByInput(symbol);
}
protected Collection getInverseArcs(Object member) {
if (member != SINK_NODE) {
return getUnminimizedFA().getArcsByTarget(member);
}
return getUnminimizedFA().getArcs();
}
protected void makeInitialBlocks() {
// sink block (for if the automaton isn't complete
makeBlock(Collections.singleton(SINK_NODE));
// accepting block
Set endNodes = getUnminimizedFA().getEndNodes();
makeBlock(endNodes);
// main block
Collection nonFinalNodes = new HashSet(getUnminimizedFA().getNodes());
nonFinalNodes.removeAll(endNodes);
makeBlock(nonFinalNodes);
}
protected void minimize() {
makeInitialBlocks();
while (hasSplit()) {
Split split = getSplit();
Collection inverseImages = getInverseImages(split);
Map inverseImagesByBlock = sortIntoBlocks(inverseImages);
for (Object o : inverseImagesByBlock.keySet()) {
Block block = (Block) o;
Collection members = (Collection) inverseImagesByBlock.get(block);
if (members.size() == 0 || members.size() == block.getMembers().size()) {
continue;
}
if (members.size() > block.getMembers().size() - members.size()) {
members = difference(block.getMembers(), members);
}
removeAll(block.getMembers(), members);
makeBlock(members);
}
}
}
public static void main(String[] args) {
/*
TransducerGraph fa = new TransducerGraph();
fa.addArc(fa.getStartNode(),"1","a","");
fa.addArc(fa.getStartNode(),"2","b","");
fa.addArc(fa.getStartNode(),"3","c","");
fa.addArc("1","4","a","");
fa.addArc("2","4","a","");
fa.addArc("3","5","c","");
fa.addArc("4",fa.getEndNode(),"c","");
fa.addArc("5",fa.getEndNode(),"c","");
System.out.println(fa);
ExactAutomatonMinimizer minimizer = new ExactAutomatonMinimizer();
System.out.println(minimizer.minimizeFA(fa));
*/
System.out.println("Starting minimizer test...");
List pathList = new ArrayList();
TransducerGraph randomFA = TransducerGraph.createRandomGraph(5000, 5, 1.0, 5, pathList);
List outputs = randomFA.getPathOutputs(pathList);
TransducerGraph.GraphProcessor quasiDeterminizer = new QuasiDeterminizer();
AutomatonMinimizer minimizer = new FastExactAutomatonMinimizer();
TransducerGraph.NodeProcessor ntsp = new TransducerGraph.SetToStringNodeProcessor(new PennTreebankLanguagePack());
TransducerGraph.ArcProcessor isp = new TransducerGraph.InputSplittingProcessor();
TransducerGraph.ArcProcessor ocp = new TransducerGraph.OutputCombiningProcessor();
TransducerGraph detGraph = quasiDeterminizer.processGraph(randomFA);
TransducerGraph combGraph = new TransducerGraph(detGraph, ocp); // combine outputs into inputs
TransducerGraph result = minimizer.minimizeFA(combGraph); // minimize the thing
System.out.println("Minimized from " + randomFA.getNodes().size() + " to " + result.getNodes().size());
result = new TransducerGraph(result, ntsp); // pull out strings from sets returned by minimizer
result = new TransducerGraph(result, isp); // split outputs from inputs
List minOutputs = result.getPathOutputs(pathList);
System.out.println("Equal? " + outputs.equals(minOutputs));
/*
randomFA = new TransducerGraph(randomFA, new TransducerGraph.OutputCombiningProcessor());
System.out.print("Starting fast minimization...");
FastExactAutomatonMinimizer minimizer2 = new FastExactAutomatonMinimizer();
Timing.startTime();
TransducerGraph minimizedRandomFA = minimizer2.minimizeFA(randomFA);
Timing.tick("done. ( "+randomFA.getArcs().size()+" arcs to "+minimizedRandomFA.getArcs().size()+" arcs)");
minimizedRandomFA = new TransducerGraph(minimizedRandomFA, new TransducerGraph.InputSplittingProcessor());
List minOutputs = minimizedRandomFA.getPathOutputs(pathList);
System.out.println("Equal? "+outputs.equals(minOutputs));
System.out.print("Starting slow minimization...");
ExactAutomatonMinimizer minimizer = new ExactAutomatonMinimizer();
Timing.startTime();
minimizedRandomFA = minimizer.minimizeFA(randomFA);
Timing.tick("done. ( "+randomFA.getArcs().size()+" arcs to "+minimizedRandomFA.getArcs().size()+" arcs)");
minimizedRandomFA = new TransducerGraph(minimizedRandomFA, new TransducerGraph.InputSplittingProcessor());
minOutputs = minimizedRandomFA.getPathOutputs(pathList);
System.out.println("Equal? "+outputs.equals(minOutputs));
*/
}
}