HP-71B Enhanced Math LEX
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01-27-2020, 08:05 AM
Post: #15
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RE: HP-71B Enhanced Math LEX
(01-26-2020 03:08 PM)Albert Chan Wrote: It take a while to find a counter-example. 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) * (X-Y) gives better result. Interesting. The 71 is using the x*x-y*y formula, as do the following Saturn-based machines since they give the same answer for your worst case test. I understand that the alternate formula (x+y)*(x-y) saves a multiplication, but does it guarantee that the result will be *always* better? Thanks for your feedback! J-F |
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