On Apr 5, 2010, at 9:44 PM, William Stein wrote:
On Mon, Apr 5, 2010 at 9:12 PM, Michael Welsh
<[email protected]> wrote:
On 6/04/2010, at 3:56 PM, Eugene Goldberg wrote:
Hello!
Here is my pyhtons results:
python
Python 2.6.5 (r265:79063, Mar 23 2010, 04:49:54)
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more
information.
1+1
2
6e-6 % 10e-6
6.0000000000000002e-06
and here is sage:
./
sage
Sage Version 4.3.5, Release Date:
2010-03-28
sage: 1+1
2
sage: 6e-6 % 10e-6
-4.00000000000000e-6
I'm sure sage is wrong.. :(
Well, at least the two answers are equivalent mod 10e-6.
They're both the same...
No they aren't.
If you type
sage: s = 6e-6
sage: s.__mod__??
then you can read the documentation for Sage's % on real numbers.
Definitely the result
sage: 6e-6 - 10e-6
-4.00000000000000e-6
matches what is claimed in the docstring. The actual function
calls the
MPFR function "mpfr_remainder", which is documented here:
http://www.mpfr.org/algorithms.pdf
See Section 3.8.
This web page: http://pyref.infogami.com/operator-mod describes the
Python
semantics for Python's __mod__ on float's. They are different than
MPFR's.
I would be in favor of following Python's conventions here--they at
least seem more natural to me (after all, % is related to "floor
division" not "round division." :)
- Robert
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