HP-71B Enhanced Math LEX

[Albert Chan]

(01-26-2020 10:54 AM)J-F Garnier Wrote:  The weakness of the z^2 operation in the HP71 Math ROM was mentioned in this article (last pages) of W. Kahan, now it is fixed!

Thanks for the update !

Replacing Z^2 as Z*Z almost always give better result.
It take a while to find a counter-example.

>X=.254661579433 @ Y=.260740997689
>COMPLEX Z @ Z = (X,Y)
>Z^2
(-3.13334783654, .132801428589)
>Z*Z
(-3.13334783655, .132801428589)

Real part of Z = X*X - Y*Y = (X+Y) * (X-Y) gives better result.
> (X+Y) * (X-Y)         ! exact value = -3.13334783654 4934739232
-3.13334783654