Comparing floats
Nobody
nobody at nowhere.com
Mon Nov 29 00:20:13 CET 2010
On Sat, 27 Nov 2010 18:23:48 -0500, Terry Reedy wrote:
>> Therefore, to implement this multiplication operation I need to have a
>> way to verify that the float tuples C and D are "equal".
>
> I might try the average relative difference:
> sum(abs((i-j)/(i+j)) for i,j in zip(C,D))/n # assuming lengths constant
The division is unstable if i and j are close to zero.
For scalars, I'd use:
abs(i-j) <= epsilon * (1 + abs(i+j))
This amounts to a relative error check for large values and an absolute
error check for values close to zero.
For a vector, I'd check that the above holds for all pairs.
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