///<summary>
/// transit prop appears as a negative literal in clause from true -> false,
/// OR prop appears as a positive literal in clause from false -> true
/// </summary>
public override void UpdateTrueNegativeAndFalsePositive(BooleanSolver b)
{
if (b.TrueDisjunctCount[Index] == 0)
{
// We just satisfied it
b.UnsatisfiedClauses.Remove(Index);
}
b.TrueDisjunctCount[Index]++;
}
///<summary>
/// transit prop appears as a negative literal in clause from false -> true,
/// OR prop appears as a positive literal in clause from true -> false
/// </summary>
public override void UpdateTruePositiveAndFalseNegative(BooleanSolver b)
{
var dCount = --b.TrueDisjunctCount[Index];
if (dCount == 0)
{
// It just transitioned from satisfied to unsatisfied
b.UnsatisfiedClauses.Add(Index);
}
}
///<summary>
/// transit prop appears as a negative literal in clause from true -> false,
/// OR prop appears as a positive literal in clause from false -> true
/// </summary>
public override void UpdateTrueNegativeAndFalsePositive(BooleanSolver b)
{
var dCount = b.TrueDisjunctCount[Index]++;
if (OneTooFewDisjuncts(dCount))
{
// We just satisfied it
b.UnsatisfiedClauses.Remove(Index);
}
else if (OneTooManyDisjuncts((ushort)(dCount + 1)))
{
// It just transitioned from satisfied to unsatisfied
b.UnsatisfiedClauses.Add(Index);
}
}
///<summary>
/// transit prop appears as a negative literal in clause from true -> false,
/// OR prop appears as a positive literal in clause from false -> true
/// </summary>
public override void UpdateTrueNegativeAndFalsePositive(BooleanSolver b)
{
var dCount = ++b.TrueDisjunctCount[Index];
var isEnabled = IsEnabled(b.Solution);
if (b.UnsatisfiedClauses.Contains(Index))
{
if (OneTooFewDisjuncts((ushort)(dCount - 1)) || !isEnabled)
{
// We just satisfied it or it was disabled
b.UnsatisfiedClauses.Remove(Index);
}
}
// I think this needs to be !IsSatisfied rather than OneTooManyDisjuncts to handle
// the case where the clause becomes enabled while it's satisfied by not at OneTooManyDisjuncts.
else if (!IsSatisfied(dCount) && isEnabled)
{
// It just transitioned from satisfied to unsatisfied, or condition just enabled
b.UnsatisfiedClauses.Add(Index);
}
}
/// <summary>
/// Find the proposition from the specified clause that will do the least damage to the clauses that are already satisfied.
/// </summary>
/// <param name="b">Current BooleanSolver</param>
/// <returns>Index of the prop to flip</returns>
public ushort GreedyFlip(BooleanSolver b)
{
// If true, the clause has too few disjuncts true
bool increaseTrueDisjuncts = IsNormalDisjunction ? b.TrueDisjunctCount[Index] <= 0 : b.TrueDisjunctCount[Index] <= MinDisjunctsMinusOne;
//Signed indices of the disjuncts of the clause
List <short> disjuncts = UnPredeterminedDisjuncts;
//Variable that was last chosen for flipping in this clause
ushort lastFlipOfThisClause = b.LastFlip[Index];
var bestCount = int.MaxValue;
var best = 0;
//Walk disjuncts in a reasonably random order
var dCount = (uint)disjuncts.Count;
var index = Random.InRange(dCount);
uint prime;
do
{
prime = Random.Prime();
} while (prime <= dCount);
for (var i = 0; i < dCount; i++)
{
var value = disjuncts[(int)index];
index = (index + prime) % dCount;
var selectedVar = (ushort)Math.Abs(value);
var truth = b.Propositions[selectedVar];
if (value < 0)
{
truth = !truth;
}
if (truth == increaseTrueDisjuncts)
{
// This is already the right polarity
continue;
}
if (selectedVar == lastFlipOfThisClause)
{
continue;
}
var threatCount = b.UnsatisfiedClauseDelta(selectedVar);
if (threatCount <= 0)
{
// Fast path - we've found an improvement; take it
// Real WalkSAT would continue searching for the best possible choice, but this
// gives better performance in my tests
// TODO - see if a faster way of computing ThreatenedClauseCount would improve things.
return(selectedVar);
}
if (threatCount < bestCount)
{
best = selectedVar;
bestCount = threatCount;
}
}
if (best == 0)
{
return((ushort)Math.Abs(disjuncts.RandomElement()));
}
return((ushort)best);
}
///<summary> /// transit prop appears as a negative literal in clause from true -> false, /// OR prop appears as a positive literal in clause from false -> true /// </summary> public abstract void UpdateTrueNegativeAndFalsePositive(BooleanSolver b);
