protected void UnitPropagate(UnitClause unit)
{
List <UnitClause> newUnitClauses = GetNewUnitClausesFromPropagate(unit);
if (newUnitClauses == null)
{
return;
}
foreach (UnitClause clause in newUnitClauses)
{
UnitPropagate(clause);
}
}
protected void PrepareBranch(UnitClause unit)
{
unsatisfiable = false;
existsNonUnitClauses = false;
UnitPropagate(unit);
if (unsatisfiable)
{
return;
}
satisfiable = !existsNonUnitClauses && CheckPolarity();
if (satisfiable)
{
return;
}
unsatisfiable = AllAssigned();
}
protected override void PrepareBranch(UnitClause unit)
{
TrailNode node = new TrailNode(unit.Index, 0);
trail.Add(node);
unsatisfiable = false;
existsNonUnitClauses = false;
UnitPropagate(unit);
if (unsatisfiable)
{
return;
}
satisfiable = !existsNonUnitClauses && CheckPolarity();
if (satisfiable)
{
return;
}
unsatisfiable = AllAssigned();
}
private bool CDCL()
{
RunInitialUnitPropagation();
UnitClause decision;
while (true)
{
// if count > 0 -> get decision, prepare
if (trail.Count > 0)
{
TrailNode last = PopTrail;
PrepareBranch(new UnitClause(last.Variable));
}
//
if (unsatisfiable)
{
if (variables.CheckPointLevel == 0)
{
return(false);
}
// analyze conflict
// addclause
// bacjump
continue;
}
if (satisfiable)
{
return(true);
}
// make decision
decision = new UnitClause(heuristic.GetVariableToBranchOn());
// false first
decision.Value *= -1;
}
}
protected List <UnitClause> GetNewUnitClausesFromPropagate(UnitClause unit)
{
if (variables[unit.Index] != 0)
{
return(null);
}
// Get clauses in which variable appears in
var clausesToScan = variableAppearances[unit.Index];
// Assign necessary variable value
variables[unit.Index] = unit.Sign;
List <UnitClause> newUnits = new List <UnitClause>();
int redundant = 0;
int removedVar = 0;
foreach (var clauseIndex in clausesToScan)
{
var clause = clauses.List[clauseIndex];
if (clause == null)
{
continue;
}
// Loop clause variables
for (int j = 0; j < clause.Count; j++)
{
if (unit.Value == clause[j] && clause.Count > 1)
{
clauses.NullifyClause(clauseIndex);
redundant++;
break;
}
if (clauses[clauseIndex, j] == -unit.Value)
{
clauses.RemoveVarAt(clauseIndex, j);
removedVar++;
j--;
}
}
clause = clauses.List[clauseIndex];
if (clause == null)
{
continue;
}
int newSize = clauses.GetClauseSize(clauseIndex);
// Created new unit clause
if (newSize == 1)
{
newUnits.Add(new UnitClause(clauses[clauseIndex, 0]));
}
else if (newSize == 0)
{
// We have propagated an empty clause
unsatisfiable = true;
}
else
{
// Some clauses have more than 1 variable, uncertain satisfiability -> must search deeper
existsNonUnitClauses = true;
}
}
// Console.WriteLine($"Ran unit propagation on {unit.Value} and redundant: {redundant}, removed vars: {removedVar}");
return(newUnits);
}