// Attempt to find a way to enforce this constraint. If successful,
// record the solution, perhaps modifying the current dataflow
// graph. Answer the constraint that this constraint overrides, if
// there is one, or nil, if there isn't.
// Assume: I am not already satisfied.
//
public Constraint satisfy(int mark)
{
chooseMethod(mark);
if (!isSatisfied())
{
if (strength == Strength.required)
{
deltablue.error("Could not satisfy a required constraint");
}
return(null);
}
// constraint can be satisfied
// mark inputs to allow cycle detection in addPropagate
markInputs(mark);
Variable outvar = output();
Constraint overridden = outvar.determinedBy;
if (overridden != null)
{
overridden.markUnsatisfied();
}
outvar.determinedBy = this;
if (!deltablue.planner.addPropagate(this, mark))
{
Console.WriteLine("Cycle encountered");
return(null);
}
outvar.mark = mark;
return(overridden);
}
// Entry point for retracting a constraint. Remove the given
// constraint and incrementally update the dataflow graph.
// Details: Retracting the given constraint may allow some currently
// unsatisfiable downstream constraint to be satisfied. We therefore collect
// a list of unsatisfied downstream constraints and attempt to
// satisfy each one in turn. This list is traversed by constraint
// strength, strongest first, as a heuristic for avoiding
// unnecessarily adding and then overriding weak constraints.
// Assume: c is satisfied.
//
public void incrementalRemove(Constraint c)
{
Variable outvar = c.output();
c.markUnsatisfied();
c.removeFromGraph();
ArrayList unsatisfied = removePropagateFrom(outvar);
Strength strength = Strength.required;
do
{
for (int i = 0; i < unsatisfied.Count; ++i)
{
Constraint u = (Constraint)unsatisfied[i];
if (u.strength == strength)
{
incrementalAdd(u);
}
}
strength = strength.nextWeaker();
} while (strength != Strength.weakest);
}
// Entry point for retracting a constraint. Remove the given
// constraint and incrementally update the dataflow graph.
// Details: Retracting the given constraint may allow some currently
// unsatisfiable downstream constraint to be satisfied. We therefore collect
// a list of unsatisfied downstream constraints and attempt to
// satisfy each one in turn. This list is traversed by constraint
// strength, strongest first, as a heuristic for avoiding
// unnecessarily adding and then overriding weak constraints.
// Assume: c is satisfied.
//
public void incrementalRemove(Constraint c)
{
Variable outvar = c.output();
c.markUnsatisfied();
c.removeFromGraph();
ArrayList unsatisfied = removePropagateFrom(outvar);
Strength strength = Strength.required;
do
{
for (int i = 0; i < unsatisfied.Count; ++i)
{
Constraint u = (Constraint)unsatisfied[i];
if (u.strength == strength)
incrementalAdd(u);
}
strength = strength.nextWeaker();
} while (strength != Strength.weakest);
}
