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public extend ( |
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| symbol | ||
| b | bool | |
| return | ||
public bool ttCheckAll(Sentence kbSentence, Sentence querySentence,
List<Symbol> symbols, Model model)
{
if (symbols.Count==0)
{
if (model.isTrue(kbSentence))
{
// System.Console.WriteLine("#");
return model.isTrue(querySentence);
}
else
{
// System.Console.WriteLine("0");
return true;
}
}
else
{
Symbol symbol = (Symbol)Util.first(symbols);
List<Symbol> rest = Util.rest(symbols);
Model trueModel = model.extend(new Symbol(symbol.getValue()), true);
Model falseModel = model.extend(new Symbol(symbol.getValue()),
false);
return (ttCheckAll(kbSentence, querySentence, rest, trueModel) && (ttCheckAll(
kbSentence, querySentence, rest, falseModel)));
}
}
public bool ttCheckAll(Sentence kbSentence, Sentence querySentence,
List <Symbol> symbols, Model model)
{
if (symbols.Count == 0)
{
if (model.isTrue(kbSentence))
{
// System.Console.WriteLine("#");
return(model.isTrue(querySentence));
}
else
{
// System.Console.WriteLine("0");
return(true);
}
}
else
{
Symbol symbol = (Symbol)Util.first(symbols);
List <Symbol> rest = Util.rest(symbols);
Model trueModel = model.extend(new Symbol(symbol.getValue()), true);
Model falseModel = model.extend(new Symbol(symbol.getValue()),
false);
return(ttCheckAll(kbSentence, querySentence, rest, trueModel) && (ttCheckAll(
kbSentence, querySentence, rest, falseModel)));
}
}
//
// PRIVATE METHODS
//
private bool dpll(List <Sentence> clauses, List <Symbol> symbols, Model model)
{
// List<Sentence> clauseList = asList(clauses);
List <Sentence> clauseList = clauses;
// System.Console.WriteLine("clauses are " + clauses.ToString());
// if all clauses are true return true;
if (areAllClausesTrue(model, clauseList))
{
// System.Console.WriteLine(model.ToString());
return(true);
}
// if even one clause is false return false
if (isEvenOneClauseFalse(model, clauseList))
{
// System.Console.WriteLine(model.ToString());
return(false);
}
// System.Console.WriteLine("At least one clause is unknown");
// try to find a unit clause
SymbolValuePair svp = findPureSymbolValuePair(clauseList, model,
symbols);
if (svp.notNull())
{
Symbol[] copy = new Symbol[symbols.Count];
symbols.CopyTo(copy);
List <Symbol> newSymbols = new List <Symbol>(copy);
newSymbols.Remove(new Symbol(svp.symbol.getValue()));
Model newModel = model.extend(new Symbol(svp.symbol.getValue()),
svp.value);
return(dpll(clauses, newSymbols, newModel));
}
SymbolValuePair svp2 = findUnitClause(clauseList, model, symbols);
if (svp2.notNull())
{
Symbol[] copy = new Symbol[symbols.Count];
symbols.CopyTo(copy);
List <Symbol> newSymbols = new List <Symbol>(copy);
newSymbols.Remove(new Symbol(svp2.symbol.getValue()));
Model newModel = model.extend(new Symbol(svp2.symbol.getValue()),
svp2.value);
return(dpll(clauses, newSymbols, newModel));
}
Symbol symbol = (Symbol)symbols[0];
// System.Console.WriteLine("default behaviour selecting " + symbol);
Symbol[] symbolsArr = new Symbol[symbols.Count];
symbols.CopyTo(symbolsArr);
List <Symbol> newSymbols2 = symbolsArr.ToList <Symbol>();
newSymbols2.RemoveAt(0);
return(dpll(clauses, newSymbols2, model.extend(symbol, true)) || dpll(
clauses, newSymbols2, model.extend(symbol, false)));
}
public void testDPLLReturnsFalseWhenOneClauseFalseInModel()
{
Model model = new Model();
model = model.extend(new Symbol("A"), true).extend(new Symbol("B"),
false);
Sentence sentence = (Sentence)parser.parse("((A OR B) AND (A => B))");
bool satisfiable = dpll.dpllSatisfiable(sentence, model);
Assert.AreEqual(false, satisfiable);
}
public void testSentenceStatusWhenPFalseAndQFalse()
{
String p = "P";
String q = "Q";
m = m.extend(new Symbol(p), false);
m = m.extend(new Symbol(q), false);
Assert.AreEqual(true, m.isFalse(andSentence));
Assert.AreEqual(true, m.isFalse(orSentence));
Assert.AreEqual(true, m.isTrue(impliedSentence));
Assert.AreEqual(true, m.isTrue(biConditionalSentence));
}
public void testDPLLFilteringNonTrueClausesGivesNullWhenAllClausesAreKnown()
{
Model model = new Model();
model = model.extend(new Symbol("A"), true).extend(new Symbol("B"),
true).extend(new Symbol("C"), true);
Sentence sentence = (Sentence)parser
.parse("((A AND B) AND (B AND C))");
List<Sentence> clauseList = new CNFClauseGatherer()
.getClausesFrom(new CNFTransformer()
.transform(sentence));
List<Sentence> clausesWithNonTrueValues = dpll
.clausesWithNonTrueValues(clauseList, model);
Assert.AreEqual(0, clausesWithNonTrueValues.Count);
}
public void testDPLLFiltersClausesTheStatusOfWhichAreKnown()
{
Model model = new Model();
model = model.extend(new Symbol("A"), true).extend(new Symbol("B"),
true);
Sentence sentence = (Sentence)parser
.parse("((A AND B) AND (B AND C))");
List<Sentence> clauseList = new CNFClauseGatherer()
.getClausesFrom(new CNFTransformer()
.transform(sentence));
List<Sentence> clausesWithNonTrueValues = dpll
.clausesWithNonTrueValues(clauseList, model);
Assert.AreEqual(1, clausesWithNonTrueValues.Count);
Sentence nonTrueClause = (Sentence)parser.parse("(B AND C)");
clausesWithNonTrueValues.Contains(nonTrueClause);
}
public Model findModelFor(String logicalSentence, int numberOfFlips,
double probabilityOfRandomWalk)
{
myModel = new Model();
Sentence s = (Sentence) new PEParser().parse(logicalSentence);
CNFTransformer transformer = new CNFTransformer();
CNFClauseGatherer clauseGatherer = new CNFClauseGatherer();
SymbolCollector sc = new SymbolCollector();
List <Symbol> symbols = sc.getSymbolsIn(s);
Random r = new Random();
for (int i = 0; i < symbols.Count; i++)
{
Symbol sym = (Symbol)symbols[i];
myModel = myModel.extend(sym, Util.randombool());
}
List <Sentence> clauses = clauseGatherer.getClausesFrom(transformer
.transform(s));
for (int i = 0; i < numberOfFlips; i++)
{
if (getNumberOfClausesSatisfiedIn(clauses, myModel) == clauses.Count)
{
return(myModel);
}
Sentence clause = clauses[random.Next(clauses.Count)];
List <Symbol> symbolsInClause = sc
.getSymbolsIn(clause);
if (random.NextDouble() >= probabilityOfRandomWalk)
{
Symbol randomSymbol = symbolsInClause[random
.Next(symbolsInClause.Count)];
myModel = myModel.flip(randomSymbol);
}
else
{
Symbol symbolToFlip = getSymbolWhoseFlipMaximisesSatisfiedClauses(
clauses,
symbolsInClause, myModel);
myModel = myModel.flip(symbolToFlip);
}
}
return(null);
}
public Model findModelFor(String logicalSentence, int numberOfFlips,
double probabilityOfRandomWalk)
{
myModel = new Model();
Sentence s = (Sentence)new PEParser().parse(logicalSentence);
CNFTransformer transformer = new CNFTransformer();
CNFClauseGatherer clauseGatherer = new CNFClauseGatherer();
SymbolCollector sc = new SymbolCollector();
List<Symbol> symbols = sc.getSymbolsIn(s);
Random r = new Random();
for (int i = 0; i < symbols.Count; i++)
{
Symbol sym = (Symbol)symbols[i];
myModel = myModel.extend(sym, Util.randombool());
}
List<Sentence> clauses = clauseGatherer.getClausesFrom(transformer
.transform(s));
for (int i = 0; i < numberOfFlips; i++)
{
if (getNumberOfClausesSatisfiedIn(clauses, myModel) == clauses.Count)
{
return myModel;
}
Sentence clause = clauses[random.Next(clauses.Count)];
List<Symbol> symbolsInClause = sc
.getSymbolsIn(clause);
if (random.NextDouble() >= probabilityOfRandomWalk)
{
Symbol randomSymbol = symbolsInClause[random
.Next(symbolsInClause.Count)];
myModel = myModel.flip(randomSymbol);
}
else
{
Symbol symbolToFlip = getSymbolWhoseFlipMaximisesSatisfiedClauses(
clauses,
symbolsInClause, myModel);
myModel = myModel.flip(symbolToFlip);
}
}
return null;
}
public void testModelEvaluation()
{
kb.tell("(NOT P11)");
kb.tell("(B11 <=> (P12 OR P21))");
kb.tell("(B21 <=> ((P11 OR P22) OR P31))");
kb.tell("(NOT B11)");
kb.tell("(B21)");
Model model = new Model();
model = model.extend(new Symbol("B11"), false);
model = model.extend(new Symbol("B21"), true);
model = model.extend(new Symbol("P11"), false);
model = model.extend(new Symbol("P12"), false);
model = model.extend(new Symbol("P21"), false);
model = model.extend(new Symbol("P22"), false);
model = model.extend(new Symbol("P31"), true);
Sentence kbs = kb.asSentence();
Assert.AreEqual(true, model.isTrue(kbs));
}
//
// PRIVATE METHODS
//
private bool dpll(List<Sentence> clauses, List<Symbol> symbols, Model model)
{
// List<Sentence> clauseList = asList(clauses);
List<Sentence> clauseList = clauses;
// System.Console.WriteLine("clauses are " + clauses.ToString());
// if all clauses are true return true;
if (areAllClausesTrue(model, clauseList))
{
// System.Console.WriteLine(model.ToString());
return true;
}
// if even one clause is false return false
if (isEvenOneClauseFalse(model, clauseList))
{
// System.Console.WriteLine(model.ToString());
return false;
}
// System.Console.WriteLine("At least one clause is unknown");
// try to find a unit clause
SymbolValuePair svp = findPureSymbolValuePair(clauseList, model,
symbols);
if (svp.notNull())
{
Symbol[] copy = new Symbol[symbols.Count];
symbols.CopyTo(copy);
List<Symbol> newSymbols = new List<Symbol>(copy);
newSymbols.Remove(new Symbol(svp.symbol.getValue()));
Model newModel = model.extend(new Symbol(svp.symbol.getValue()),
svp.value);
return dpll(clauses, newSymbols, newModel);
}
SymbolValuePair svp2 = findUnitClause(clauseList, model, symbols);
if (svp2.notNull())
{
Symbol[] copy = new Symbol[symbols.Count];
symbols.CopyTo(copy);
List<Symbol> newSymbols = new List<Symbol>(copy);
newSymbols.Remove(new Symbol(svp2.symbol.getValue()));
Model newModel = model.extend(new Symbol(svp2.symbol.getValue()),
svp2.value);
return dpll(clauses, newSymbols, newModel);
}
Symbol symbol = (Symbol)symbols[0];
// System.Console.WriteLine("default behaviour selecting " + symbol);
Symbol[] symbolsArr = new Symbol[symbols.Count];
symbols.CopyTo(symbolsArr);
List<Symbol> newSymbols2 = symbolsArr.ToList<Symbol>();
newSymbols2.RemoveAt(0);
return (dpll(clauses, newSymbols2, model.extend(symbol, true)) || dpll(
clauses, newSymbols2, model.extend(symbol, false)));
}
public void testComplexSentence()
{
String p = "P";
String q = "Q";
m = m.extend(new Symbol(p), true);
m = m.extend(new Symbol(q), false);
Sentence sent = (Sentence)parser.parse("((P OR Q) AND (P => Q))");
Assert.IsFalse(m.isTrue(sent));
Assert.IsTrue(m.isFalse(sent));
Sentence sent2 = (Sentence)parser.parse("((P OR Q) AND (Q))");
Assert.IsFalse(m.isTrue(sent2));
Assert.IsTrue(m.isFalse(sent2));
}
public void testDPLLFindsPurePositiveSymbolsWhenTheyExist()
{
Model model = new Model();
model = model.extend(new Symbol("A"), true).extend(new Symbol("B"),
true);
Sentence sentence = (Sentence)parser
.parse("((A AND B) AND (B AND C))");
List<Sentence> clauseList = new CNFClauseGatherer()
.getClausesFrom(new CNFTransformer()
.transform(sentence));
List<Symbol> symbolList = new SymbolCollector().getSymbolsIn(sentence);
DPLL.SymbolValuePair sv = dpll.findPureSymbolValuePair(clauseList,
model, symbolList);
Assert.IsNotNull(sv);
Assert.AreEqual(new Symbol("C"), sv.symbol);
Assert.AreEqual(true, sv.value);
}
