Feature suggestion: sum() ought to use a compensated summation algorithm

[Arnaud Delobelle]

Szabolcs Horvát <szhorvat at gmail.com> writes:

[...]
> A little research shows that Mathematica uses a "compensated
> summation" algorithm.  Indeed, using the algorithm described at
> http://en.wikipedia.org/wiki/Kahan_summation_algorithm
> gives us a result around ~ 10^-17:
>
> def compSum(arr):
>     s = 0.0
>     c = 0.0
>     for x in arr:
>         y = x-c
>         t = s+y
>         c = (t-s) - y
>         s = t
>     return s
>
> mean = compSum(data)/len(data)
> print compSum(x - mean for x in data)/len(data)
>
>
> I thought that it would be very nice if the built-in sum() function
> used this algorithm by default.  Has this been brought up before?
> Would this have any disadvantages (apart from a slight performance
> impact, but Python is a high-level language anyway ...)?
>
> Szabolcs Horvát

sum() works for any sequence of objects with an __add__ method, not
just floats!  Your algorithm is specific to floats.

-- 
Arnaud