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[poincare/logarithm] ln(0) = undef

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As a consequence, log(x,0) = ln(x)/ln(0) = undef
This commit is contained in:
Gabriel Ozouf
2020-12-01 17:52:32 +01:00
committed by LeaNumworks
parent 71ac56f8a7
commit 9775953142
1 changed files with 13 additions and 33 deletions
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46
poincare/src/logarithm.cpp
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@@ -267,48 +267,20 @@ Expression Logarithm::shallowReduce(ExpressionNode::ReductionContext reductionCo
Expression Logarithm::simpleShallowReduce(ExpressionNode::ReductionContext reductionContext) {
Expression c = childAtIndex(0);
Expression b = childAtIndex(1);
// log(0,0)->Undefined
if (c.type() == ExpressionNode::Type::Rational && b.type() == ExpressionNode::Type::Rational && static_cast<Rational &>(b).isZero() && static_cast<Rational &>(c).isZero()) {
return replaceWithUndefinedInPlace();
}
// log(x,1)->Undefined
if (b.type() == ExpressionNode::Type::Rational && static_cast<Rational &>(b).isOne()) {
return replaceWithUndefinedInPlace();
}
bool infiniteArg = c.recursivelyMatches(Expression::IsInfinity, reductionContext.context());
// log(x,x)->1 with x != inf and log(inf,inf) = undef
if (c.isIdenticalTo(b)) {
Expression result = infiniteArg ? Undefined::Builder().convert<Expression>() : Rational::Builder(1).convert<Expression>();
replaceWithInPlace(result);
return result;
}
// log(x,0)->0 with x != inf and log(inf,0) = undef
// log(x,0) -> undef
if (b.type() == ExpressionNode::Type::Rational && static_cast<Rational &>(b).isZero()) {
Expression result = infiniteArg ? Undefined::Builder().convert<Expression>() : Rational::Builder(0).convert<Expression>();
replaceWithInPlace(result);
return result;
return replaceWithUndefinedInPlace();
}
if (c.type() == ExpressionNode::Type::Rational) {
const Rational r = static_cast<Rational &>(c);
// log(0, x) = -inf if x > 1 && x != inf || inf x < 1 || undef if x < 0
// log(0, x) = undef
if (r.isZero()) {
bool infiniteBase = b.recursivelyMatches(Expression::IsInfinity, reductionContext.context());
// Special case: log(0,inf) -> undef
if (infiniteBase) {
return replaceWithUndefinedInPlace();
}
bool isNegative = true;
Expression result;
Evaluation<float> baseApproximation = b.node()->approximate(1.0f, ExpressionNode::ApproximationContext(reductionContext, true));
std::complex<float> logDenominator = std::log10(static_cast<Complex<float>&>(baseApproximation).stdComplex());
if (logDenominator.imag() != 0.0f || logDenominator.real() == 0.0f) {
result = Undefined::Builder();
}
isNegative = logDenominator.real() > 0.0f;
result = result.isUninitialized() ? Infinity::Builder(isNegative) : result;
replaceWithInPlace(result);
return result;
return replaceWithUndefinedInPlace();
}
// log(1) = 0;
if (r.isOne()) {
@@ -317,6 +289,14 @@ Expression Logarithm::simpleShallowReduce(ExpressionNode::ReductionContext reduc
return result;
}
}
bool infiniteArg = c.recursivelyMatches(Expression::IsInfinity, reductionContext.context());
// log(x,x)->1 with x != inf and log(inf,inf) = undef
if (c.isIdenticalTo(b)) {
Expression result = infiniteArg ? Undefined::Builder().convert<Expression>() : Rational::Builder(1).convert<Expression>();
replaceWithInPlace(result);
return result;
}
return *this;
}