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[poincare] Fix Power::compute precision on real numbers

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Fix bug: if we define f(x) = x^3-x-6, f(2) was not equal to 0 in the
values table
This commit is contained in:
Émilie Feral
2018-12-06 14:47:24 +01:00
committed by LeaNumworks
parent f7193602ef
commit 2d97b43e63
1 changed files with 11 additions and 6 deletions
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17
poincare/src/power.cpp
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@@ -82,14 +82,19 @@ int PowerNode::getPolynomialCoefficients(Context & context, const char * symbolN
template<typename T>
Complex<T> PowerNode::compute(const std::complex<T> c, const std::complex<T> d) {
std::complex<T> result = std::pow(c, d);
std::complex<T> result;
if (c.imag() == 0.0 && d.imag() == 0.0 && c.real() >= 0.0) {
/* pow: (R+, R) -> R+
* However, std::pow(2.0, 1000) = (INFINITY, NAN). Openbsd pow of a
* positive real and another real has a undefined imaginary when the real
* result is infinity. To avoid this, we force the imaginary part of
* pow(R+,R) to 0.0. */
result.imag(0.0);
* For pow on (R+,R) we rather use std::pow(double, double) because:
* - pow on complexes is not as precise as pow on double: for instance,
* pow(complex<double>(2.0,0.0), complex<double>(3.0,0.0) = complex(7.9999999999999982,0.0)
* and pow(2.0,3.0) = 8.0
* - Using complex pow, std::pow(2.0, 1000) = (INFINITY, NAN).
* Openbsd pow of a positive real and another real has a undefined
* imaginary when the real result is infinity. */
result = std::complex<T>(std::pow(c.real(), d.real()));
} else {
result = std::pow(c, d);
}
/* Openbsd trigonometric functions are numerical implementation and thus are
* approximative.