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[poincare] Power: avoid infinite loop of reduction

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2^(1/2+a) --> 2^(1/2)*2^a --> 2^(1/2+a)-->...
This commit is contained in:
Émilie Feral
2018-12-26 16:42:15 +01:00
committed by Léa Saviot
parent 2268817738
commit e265b0319c
1 changed files with 17 additions and 3 deletions
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20
poincare/src/power.cpp
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@@ -622,7 +622,7 @@ Expression Power::shallowReduce(Context & context, Preferences::ComplexFormat co
}
}
}
// Step 12: a^(b+c+...) -> Rational(a^b)*a^c with a and b rational and a != 0
// Step 12: a^(p/q+c+...) -> Rational(a^p)*a^(1/q+c+...) with a rational and a != 0 and p, q integers
if (!letPowerAtRoot
&& childAtIndex(0).type() == ExpressionNode::Type::Rational
&& !childAtIndex(0).convert<Rational>().isZero()
@@ -631,12 +631,26 @@ Expression Power::shallowReduce(Context & context, Preferences::ComplexFormat co
Addition a = childAtIndex(1).convert<Addition>();
// Check is b is rational
if (a.childAtIndex(0).type() == ExpressionNode::Type::Rational) {
const Rational rationalBase = childAtIndex(0).convert<Rational>();
const Rational rationalIndex = a.childAtIndex(0).convert<Rational>();
if (rationalIndex.unsignedIntegerNumerator().isOne() && !rationalIndex.integerDenominator().isOne()) {
/* Do not reduce a^(1/q+c+...) to avoid potential infinite loop:
* a^(1/q+c+...) --> a^(1/q)*a^(c+...) --> a^(1/q+c+...)*/
/* TODO: do something more sensible here:
* - add rule (-rational)^x --> (-1)^x*rational^x so we only consider
* positive rational or (-1)
* - change simplifyRationalRationalPower to be able to detect when no
* rational was extracted (ie 2^(1/2) --> 2^(1/2)) to avoid applying
* this rule in that case
* Once this is done, we can reduce 4^(1/2+a) --> 2*4^a which is not
* done so far to avoir the infinite loop:
* 2^(1/2+s) --> 2^(1/2)*2^s --> 2^(1/2+s)... */
return *this;
}
const Rational rationalBase = childAtIndex(0).convert<Rational>();
if (RationalExponentShouldNotBeReduced(rationalBase, rationalIndex)) {
return *this;
}
Power p1 = Power(childAtIndex(0).clone(), a.childAtIndex(0).clone());
Power p1 = Power(childAtIndex(0).clone(), a.childAtIndex(0));
Power thisRef = *this;
childAtIndex(1).convert<Addition>().removeChildAtIndexInPlace(0); // p2 = a^(c+...)
// if addition had only 2 children