2 Aug
2015
2 Aug
'15
8:59 p.m.
Hi,
I noticed that
evalf( (-1)^(1/3) )
gives
0.5+0.86602540378443864673*I
Is there any way to tell GiNaC to return the real root by default? There isn't. GiNaC, like almost all other systems, returns the solution on the principal branch, compatible with exp(log(-1)/3). I suppose there is some excellent mathematical reason for this...but for me it means that I can't use GiNaC to verify Cardano's formula for a cubic function:
x = (-1 - sqrt(2))^(1/3) + (-1 + sqrt(2))^(1/3); (-1-sqrt(2))^(1/3)+(-1+sqrt(2))^(1/3)
evalf(x^3 + 3 * x + 2); 3.3544445609126528848+8.9073474964875349776*I
Surely there must be a way to verify such a formula in GiNaC??? Jan