/// <summary>
///<code>
/// procedure OTTER(sos, usable)
/// inputs: sos, a set of support-clauses defining the problem (a global variable)
/// usable, background knowledge potentially relevant to the problem
///</code>
/// </summary>
/// <param name="ansHandler"></param>
/// <param name="idxdClauses"></param>
/// <param name="sos"></param>
/// <param name="usable"></param>
/// <returns></returns>
private IInferenceResult Otter(OTTERAnswerHandler ansHandler,
IndexedClauses idxdClauses, ISet<Clause> sos, ISet<Clause> usable)
{
LightestClauseHeuristic.InitialSOS(sos);
// * repeat
do {
// * clause <- the lightest member of sos
Clause clause = LightestClauseHeuristic.GetLightestClause();
if (null != clause)
{
// * move clause from sos to usable
sos.Remove(clause);
LightestClauseHeuristic.RemovedClauseFromSOS(clause);
usable.Add(clause);
// * PROCESS(INFER(clause, usable), sos)
this.Process(ansHandler, idxdClauses, this.Infer(clause, usable), sos, usable);
}
// * until sos = [] or a refutation has been found
}
while (sos.Count != 0 && !ansHandler.IsComplete());
return ansHandler;
}
// procedure PROCESS(clauses, sos)
private void Process(OTTERAnswerHandler ansHandler,
IndexedClauses idxdClauses, ISet<Clause> clauses, ISet<Clause> sos,
ISet<Clause> usable) {
// * for each clause in clauses do
foreach (Clause clause in clauses)
{
// * clause <- SIMPLIFY(clause)
var simplifiedClause = ClauseSimplifier.Simplify(clause);
// * merge identical literals
// Note: Not required as handled by Clause Implementation
// which keeps literals within a ISet, so no duplicates
// will exist.
// * discard clause if it is a tautology
if (simplifiedClause.IsTautology())
{
continue;
}
// * if clause has no literals then a refutation has been found
// or if it just Contains the answer literal.
if (!ansHandler.IsAnswer(simplifiedClause))
{
// * sos <- [clause | sos]
// This check ensure duplicate clauses are not
// introduced which will cause the
// ILightestClauseHeuristic to loop continuously
// on the same pair of objects.
if (!sos.Contains(simplifiedClause) && !usable.Contains(simplifiedClause))
{
foreach (var ac in
simplifiedClause.GetFactors().Where(ac => !sos.Contains(ac) && !usable.Contains(ac)))
{
idxdClauses.addClause(ac, sos, usable);
// * if clause has one literal then look for unit
// refutation
this.LookForUnitRefutation(ansHandler, idxdClauses, ac,
sos, usable);
}
}
}
if (ansHandler.IsComplete())
{
break;
}
}
}
private void LookForUnitRefutation(OTTERAnswerHandler ansHandler,
IndexedClauses idxdClauses, Clause clause, ISet<Clause> sos,
ISet<Clause> usable)
{
ISet<Clause> toCheck = new HashedSet<Clause>();
if (ansHandler.IsCheckForUnitRefutation(clause))
{
foreach (Clause s in sos)
{
if (s.IsUnitClause())
{
toCheck.Add(s);
}
}
foreach (Clause u in usable)
{
if (u.IsUnitClause())
{
toCheck.Add(u);
}
}
}
if (toCheck.Count > 0)
{
toCheck = this.Infer(clause, toCheck);
foreach (Clause t in toCheck)
{
// * clause <- SIMPLIFY(clause)
var simplifiedT = ClauseSimplifier.Simplify(t);
// * discard clause if it is a tautology
if (simplifiedT.IsTautology())
{
continue;
}
// * if clause has no literals then a refutation has been found
// or if it just Contains the answer literal.
if (!ansHandler.IsAnswer(simplifiedT))
{
// * sos <- [clause | sos]
// This check ensure duplicate clauses are not
// introduced which will cause the
// ILightestClauseHeuristic to loop continuously
// on the same pair of objects.
if (!sos.Contains(simplifiedT) && !usable.Contains(simplifiedT))
{
idxdClauses.addClause(simplifiedT, sos, usable);
}
}
if (ansHandler.IsComplete())
{
break;
}
}
}
}
