# Array#float_sum (like math.fsum of Python)

Issue #10298 has been updated by Akira T…

It is not fit to Array class because Array is not only for Float.

I think it is better to implement it as an optimization of reduce(:+).

Feature #10298: Array#float_sum (like math.fsum of Python)
https://bugs.ruby-lang.org/issues/10298#change-49376

• Author: Takeshi Nishimatsu
• Status: Open
• Priority: Low
• Assignee:
• Category: math
• Target version:

Here, I propose Array#float_sum in array.c (or math.c).
Array#float_sum returns an accurate total summation of Float
elements in an array using the Kahan summation algorithm
http://en.wikipedia.org/wiki/Kahan_summation_algorithm .
This algorithm can significantly reduce the numerical
error in the total obtained by adding a sequence of
finite precision floating point numbers, compared to the
obvious approach. Python already have math.fsum
https://docs.python.org/2/library/math.html#math.fsum .

``````[0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1].float_sum   #=> 1.0
[].float_sum                                                   #=> 0.0
Array.new( 10, 0.1).float_sum    #=>  1.0
Array.new(100, 0.1).float_sum    #=> 10.0
# cf.
Array.new( 10, 0.1).reduce(:+)   #=>  0.9999999999999999
Array.new(100, 0.1).reduce(:+)   #=>  9.99999999999998
``````

The name of method can be fsum, sum_float, etc., though
I propose float_sum.

This Array#float_sum is inspired by Feature #9834
Float#{next_float,prev_float}.

—Files--------------------------------
array.float_sum.patch (1.32 KB)