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[poincare] Power: always reduce (a^b)^(-1)

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This commit is contained in:
Émilie Feral
2019-11-13 14:49:44 +01:00
committed by LeaNumworks
parent cfdc6344bf
commit 6135fced52
2 changed files with 10 additions and 5 deletions
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14
poincare/src/power.cpp
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@@ -625,18 +625,22 @@ Expression Power::shallowReduce(ExpressionNode::ReductionContext reductionContex
* --> tan(2)+tan(2)*[tan(2)^1/2]^(-1)/tan(2)
* --> tan(2)^(3/2)+tan(2)^(3/2)*[tan(2)^1/2]^(-1)/tan(2)^3/2
* --> ...
* Indeed, we have to apply the rule (a^b)^c -> a^(b*c) as soon as c is an
* integer.
* Indeed, we have to apply the rule (a^b)^c -> a^(b*c) as soon as c is -1.
*/
if (baseType == ExpressionNode::Type::Power) {
Power powerBase = static_cast<Power &>(base);
bool cInteger = indexType == ExpressionNode::Type::Rational && static_cast<Rational &>(index).isInteger();
bool applyRule = powerBase.childAtIndex(0).sign(reductionContext.context()) == ExpressionNode::Sign::Positive // a > 0
|| (indexType == ExpressionNode::Type::Rational && static_cast<Rational &>(index).isInteger()); // c integer
|| cInteger; // c integer
bool cMinusOne = cInteger && static_cast<Rational &>(index).isMinusOne();
/* If the complexFormat is real, we check that the inner power is defined
* before applying the rule (a^b)^c -> a^(b*c). Otherwise, we return
* 'unreal' or we do nothing. */
if (reductionContext.complexFormat() == Preferences::ComplexFormat::Real) {
* 'unreal' or we do nothing.
* We escape this additional check if c = -1 for two reasons:
* - (a^b)^(-1) has to be reduced to avoid infinite loop discussed above;
* - if a^b is unreal, a^(-b) also. */
if (!cMinusOne && reductionContext.complexFormat() == Preferences::ComplexFormat::Real) {
Expression approximation = powerBase.approximate<float>(reductionContext.context(), reductionContext.complexFormat(), reductionContext.angleUnit());
if (approximation.type() == ExpressionNode::Type::Unreal) {
// The inner power is unreal, return "unreal"

1
poincare/test/simplification.cpp
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@@ -107,6 +107,7 @@ QUIZ_CASE(poincare_simplification_infinity) {
}
QUIZ_CASE(poincare_simplification_addition) {
assert_parsed_expression_simplify_to("1/x^2+3", "\u00123×x^2+1\u0013/x^2", User, Radian, Real);
assert_parsed_expression_simplify_to("1+x", "x+1");
assert_parsed_expression_simplify_to("1/2+1/3+1/4+1/5+1/6+1/7", "223/140");
assert_parsed_expression_simplify_to("1+x+4-i-2x", "-i-x+5");