protected override bool Update(NumericVariable v)
{
return(v.RestrictRange(-(v == _variable1 ? _variable2 : _variable1).Value));
}
//public SumIs0Constraint Plus(DoubleHolder d) {
// return new SumIs0Constraint(_plus.Concat(new[] { d }));
//}
protected override bool Update(NumericVariable v)
{
bool changed = false;
// The following propagation uses these ideas:
// For each variable v, take the sum S of all OTHER Lo values. A high value that is higher
// than -S will never cancel S to zero, let alone sums that are greater than S. Hence,
// v.Hi can be restricted to <= -S.
// Likewise, v.Lo can be restricted to >= -S where S is the sum of all other Hi values.
// O(n^2) algorithm - a O(n) algorithm is possible ... later
double loSum = 0;
// OnceExcluded is necessary for a constraint like X + X + Y = 0: When we already know
// that X = [100..100] and Y = [-200..-200], this should succeed. However, when during
// Upgrade(X) we skip both X's (via w != v), the sum will not be 100-200 == 100, but
// -200; and hence
// X will then be restricted to [200..+inf], which, together with the previously known
// value X = 100 will erroneously imply that there is no solution for X.
// By the way, when in X + X + Y = 0, we have X = [-inf...+inf] and Y = [-200..-200] at
// the beginning, we will NOT conclude that X = [100..100] - that would be equation
// solving, which we do not support at this level.
bool onceExcluded = false;
foreach (var w in _inputVariables)
{
if (onceExcluded || w != v)
{
double wLo = w.Value.Lo;
if (double.IsNegativeInfinity(wLo))
{
// Nothing can be said about the sum of lows - cancel this computation;
goto SKIP_LO;
}
loSum += wLo;
}
else
{
onceExcluded = true;
}
}
changed |= v.RestrictRange(double.NegativeInfinity, -loSum);
SKIP_LO:
double hiSum = 0;
onceExcluded = false;
foreach (var w in _inputVariables)
{
if (onceExcluded || w != v)
{
double wHi = w.Value.Hi;
if (double.IsPositiveInfinity(wHi))
{
// Nothing can be said about the sum of his - cancel this computation;
goto SKIP_HI;
}
hiSum += wHi;
}
else
{
onceExcluded = true;
}
}
changed |= v.RestrictRange(-hiSum, double.PositiveInfinity);
SKIP_HI:
return(changed);
}
protected override bool Update(NumericVariable v)
{
return(v.RestrictRange(_range));
}