On Jul 7, 2010, at 9:08 AM, Thomas Jollans wrote:
On 07/07/2010 02:05 PM, david mainzer wrote:
today i create some slides about floating point arithmetic. I used an
example from
http://docs.python.org/tutorial/floatingpoint.html
so i start the python shell on my linux machine:
d...@maxwell $ python
Python 2.6.5 (release26-maint, May 25 2010, 12:37:06)
[GCC 4.3.4] on linux2
Type "help", "copyright", "credits" or "license" for more
information.
sum = 0.0
for i in range(10):
... sum += 0.1
...
sum
0.99999999999999989
But thats looks a little bit wrong for me ... i must be a number
greater
then 1.0 because 0.1 =
0.100000000000000005551115123125782702118158340454101562500000000000
in python ... if i print it.
The simple fact of the matter is: floating point arithmetic isn't
accurate. This has nothing to do with Python, it's the fault of your
processor's floating point handling. It's good enough in most cases,
but
you should never rely on a floating-point number to have exactly a
certain value. It won't work.
Yes, this might be a good time to review the dense but interesting
document, "What Every Computer Scientist Should Know About Floating-
Point Arithmetic":
http://docs.sun.com/source/806-3568/ncg_goldberg.html
Cheers
Philip
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