on floating-point numbers
Schachner, Joseph
Joseph.Schachner at Teledyne.com
Fri Sep 3 12:05:00 EDT 2021
Actually, Python has an fsum function meant to address this issue.
>>> math.fsum([1e14, 1, -1e14])
1.0
>>>
Wow it works.
--- Joseph S.
Teledyne Confidential; Commercially Sensitive Business Data
-----Original Message-----
From: Hope Rouselle <hrouselle at jevedi.com>
Sent: Thursday, September 2, 2021 9:51 AM
To: python-list at python.org
Subject: on floating-point numbers
Just sharing a case of floating-point numbers. Nothing needed to be solved or to be figured out. Just bringing up conversation.
(*) An introduction to me
I don't understand floating-point numbers from the inside out, but I do know how to work with base 2 and scientific notation. So the idea of expressing a number as
mantissa * base^{power}
is not foreign to me. (If that helps you to perhaps instruct me on what's going on here.)
(*) A presentation of the behavior
>>> import sys
>>> sys.version
'3.8.10 (tags/v3.8.10:3d8993a, May 3 2021, 11:48:03) [MSC v.1928 64 bit (AMD64)]'
>>> ls = [7.23, 8.41, 6.15, 2.31, 7.73, 7.77]
>>> sum(ls)
39.599999999999994
>>> ls = [8.41, 6.15, 2.31, 7.73, 7.77, 7.23]
>>> sum(ls)
39.60000000000001
All I did was to take the first number, 7.23, and move it to the last position in the list. (So we have a violation of the commutativity of
addition.)
Let me try to reduce the example. It's not so easy. Although I could display the violation of commutativity by moving just a single number in the list, I also see that 7.23 commutes with every other number in the list.
(*) My request
I would like to just get some clarity. I guess I need to translate all these numbers into base 2 and perform the addition myself to see the situation coming up?
More information about the Python-list
mailing list