HP71B Enhanced Math LEX

01272020, 08:05 AM
Post: #15




RE: HP71B Enhanced Math LEX
(01262020 03:08 PM)Albert Chan Wrote: It take a while to find a counterexample. Nice finding of a worst case for z*z, thanks! I believe that the z^2 result is better just by chance. How did you find it? I'm guessing just brute force? Anyway, the next 3 digits are 493, very close to the limit for up/down rounding, so we may say that both answers are equally right :) Quote:Real part of Z = X*X  Y*Y = (X+Y) * (XY) gives better result. Interesting. The 71 is using the x*xy*y formula, as do the following Saturnbased machines since they give the same answer for your worst case test. I understand that the alternate formula (x+y)*(xy) saves a multiplication, but does it guarantee that the result will be *always* better? Thanks for your feedback! JF 

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