Hp 50g - "?" message and CAS bugs

[ttw]

(11-03-2020 04:30 PM)Albert Chan Wrote:  

(11-03-2020 08:48 AM)Carsen Wrote:  In short, this is by design. Although, it does not answer why it is designed this way.

With sgn(x) = x/abs(x), symbolic manipulations are simpler.

Hp50g> 'X+SIN(X)'
Hp50g> SIGN             → (X+SIN(X)) / |X+SIN(X)|

Adding sgn(0)=0 rule, we get this:

IFTE(X+SIN(X) , (X+SIN(X)) / |X+SIN(X)| , 0)

The problem arises in the context of integer computations though. It means an extra test for every comparison.