// Find the best pivot in column j.
private KeyValuePair <int, Real> PartialPivot(int i1, int i2, Expression j)
{
int row = -1;
Real max = -1;
for (int i = i1; i < i2; ++i)
{
Expression ij = equations[i][j];
if (!ij.EqualsZero())
{
// If we don't a pivot yet, just grab this one.
if (row == -1)
{
row = i;
}
// Select the larger pivot if this is a constant.
if (ij is Constant && Real.Abs((Real)ij) > max)
{
row = i;
max = Real.Abs((Real)ij);
}
}
}
return(new KeyValuePair <int, Real>(row, max));
}
public override bool Matches(Expression E, MatchContext Matched)
{
Expression matched;
if (Matched.TryGetValue(Right, out matched))
{
if (Left.Matches(E ^ Binary.Divide(1, matched), Matched))
{
return(true);
}
}
// x^0 = 1.
if (E.EqualsOne() && Right.Matches(0, Matched))
{
return(true);
}
// 0^x = 0.
if (E.EqualsZero() && Left.Matches(0, Matched))
{
return(true);
}
Binary PE = E as Power;
if (!ReferenceEquals(PE, null) && Matched.TryMatch(() => Left.Matches(PE.Left, Matched) && Right.Matches(PE.Right, Matched)))
{
return(true);
}
// If the exponent matches 1, E can match left.
if (Matched.TryMatch(() => Right.Matches(1, Matched) && Left.Matches(E, Matched)))
{
return(true);
}
if (Right.IsInteger() && Left.Matches(ComputerAlgebra.Power.New(E, Binary.Divide(1, Right)).Evaluate(), Matched))
{
return(true);
}
return(false);
}
// Find the best pivot in column j.
private KeyValuePair <int, Real> PartialPivot(int i1, int i2, Expression j, IEnumerable <Arrow> PivotConditions)
{
int row = -1;
Real max = -1;
for (int i = i1; i < i2; ++i)
{
Expression ij = equations[i][j];
if (!ij.EqualsZero())
{
// If we don't a pivot yet, just grab this one.
if (row == -1)
{
row = i;
}
// Select the larger pivot if this is a constant, using the PivotConditions.
Expression ijc;
if (ij is Constant || PivotConditions is null)
{
ijc = ij;
}
else
{
ijc = ij.Evaluate(PivotConditions);
}
if (ijc is Constant && Real.Abs((Real)ijc) > max)
{
row = i;
max = Real.Abs((Real)ijc);
}
}
}
return(new KeyValuePair <int, Real>(row, max));
}
public override bool Matches(Expression E, MatchContext Matched)
{
// if E is zero, any term can match to zero to succeed.
if (E.EqualsZero())
{
return(Terms.Any(i => i.Matches(0, Matched)));
}
// Move the constants in this pattern to E.
IEnumerable <Expression> PTerms = Terms;
IEnumerable <Expression> Constants = PTerms.OfType <Constant>();
if (Constants.Any())
{
E = Binary.Divide(E, New(Constants)).Evaluate();
PTerms = PTerms.Except(Constants, RefComparer);
}
IEnumerable <Expression> ETerms = TermsOf(E);
// Try starting the match at each term of the pattern.
foreach (Expression p in PTerms)
{
// Remaining terms of the pattern.
Expression P = New(PTerms.ExceptUnique(p, RefComparer));
// If p is a variable, we have to handle the possibility that more than one term of E might match this term.
if (p is Variable)
{
// Check if p has already been matched. If it has, treat it as a constant and match the rest of the terms.
Expression matched;
if (Matched.TryGetValue(p, out matched))
{
// p has already been matched. Remove it out of E and match the remainder of the pattern.
if (P.Matches(E / matched, Matched))
{
return(true);
}
}
else
{
// Try matching p to the various combinations of the terms of E.
for (int i = 1; i <= ETerms.Count(); ++i)
{
foreach (IEnumerable <Expression> e in ETerms.Combinations(i))
{
if (Matched.TryMatch(() =>
p.Matches(New(e), Matched) &&
P.Matches(New(ETerms.ExceptUnique(e, RefComparer)), Matched)))
{
return(true);
}
}
}
// Try matching p to identity.
if (Matched.TryMatch(() => p.Matches(1, Matched) && P.Matches(E, Matched)))
{
return(true);
}
}
}
else
{
// If p is not a variable, try matching it to any of the terms of E.
foreach (Expression e in ETerms)
{
if (Matched.TryMatch(() =>
p.Matches(e, Matched) &&
P.Matches(New(ETerms.ExceptUnique(e, RefComparer)), Matched)))
{
return(true);
}
}
}
}
return(false);
}
