Ans and ^ (1/3)

[BartDB]

(03-30-2015 06:15 PM)John Colvin Wrote:  

(03-30-2015 04:08 PM)Helge Gabert Wrote:  I ran into this a while back, but didn't get around to posting

Let's say some calculation results in a negative number, like 7-8.2 = -1.2

Pressing x^y (1/3), using built-in Ans, results in one of the two complex roots of the polynomial x^3+1.2 being returned.

But . . . typing -1.2^ (1/3) results in the real root being returned.

How come this different behavior of Ans^(1/3) vis-a-vis the explicit, typed result?

CAS settings: simplify min, exact, use sqrt, principal, use i.

This inconsistency also occurs in RPN mode. It might be something to do with raising the number to the 1/3 power vs. taking the cube root. For example if I place -8 on the stack and then 1/3 on the stack and hit the x^y key I get a complex root, but if I place -8^(1/3) on the stack I get -2 after pressing eval.

> It might be something to do with raising the number to the 1/3 power vs. taking the cube root.

No, it has to do with operator precedence of a typed in number vs. a variable. See my other post.

In RPN mode, in the first case you place -8 on level-2 and 1/3 on the level-1 and press x^y which results in (level-2)^(level-1), i.e. again -8 is the level-2 variable as a whole.
In the second case you are entering an equation like format so again power before minus.

Best regards.