HP-35’s x^y Why?

[robve]

(11-03-2021 07:47 AM)J-F Garnier Wrote:  Example on Saturn-based HP machines:
125^(1/3) = 4.9999...
but XROOT(125,3)=5 exactly.

Wow. This is even worse, if true:

125^(1/3) = EXP(1/3*LOG(125)) and XROOT(125,3) = EXP(LOG(125)/3) yet somehow these differ on Saturn-based HP machines. Roundoff issues.

This cheap Casio gets it right:

Casio fx-115ES plus
(-128)^(1/7)=-2 OK
(-128)^(.1428571429) ERROR (as can be expected)

- Rob

EDIT: not entirely surprising for the Casio fx-115ES plus, because this model supports exact rationals i.e. 1/3 is exact and 1/(1/3)=3 exactly.