[Numpy-discussion] Re: numpy, overflow, inf, ieee, and rich , comparison
Johann Hibschman
johann at physics.berkeley.edu
Fri Oct 27 19:49:07 EDT 2000
- Previous message (by thread): [Numpy-discussion] Re: numpy, overflow, inf, ieee, and rich , comparison
- Next message (by thread): [Numpy-discussion] Re: numpy, overflow, inf, ieee, and rich , comparison
- Messages sorted by:
[ date ]
[ thread ]
[ subject ]
[ author ]
Darren New writes:
> Johann Hibschman wrote:
>> What's 'remainder', if not the same as 'modulo'?
> The problem is with negatives. X mod 7 is between 0 and 6 (inclusive) for
> all X.
> -3 mod 7 != 3 and -3 mod 7 != -3.
> -3 mod 7 = 4. -1 mod 7 = 6.
Oh, okay. I thought that was a given for any mod/remainder function.
So there's no problem with the python implementation, then? I thought
you were implying that there was.
> That's the definition of mod, and that's the semantics I find useful.
> Note: I don't think there *is* a definition for mod that handles a negative
> number as the second argument.
Well, there's the least positive residue that I mentioned before; I'm
used to seeing that one. Congruence modulo m is defined for negative
m, i.e. a = b mod m iff m divides (a-b). So all you have to do is
pick which congruent number you want, and the "least positive" rule
works for that.
Python seems to pick the "least negative" when m < 0, which is kinda
weird, but at least consistent.
>> "r = a % m" should preferrably be in the range from 0 < r < |m|,
>> right?
> Well, 0 <= r < |m| I would guess.
Right. Oops.
(I've gotta avoid getting drawn into these math discussions, or I'll
have to invoke Sarah again, and Ping will mock me.)
--
Johann Hibschman johann at physics.berkeley.edu
- Previous message (by thread): [Numpy-discussion] Re: numpy, overflow, inf, ieee, and rich , comparison
- Next message (by thread): [Numpy-discussion] Re: numpy, overflow, inf, ieee, and rich , comparison
- Messages sorted by:
[ date ]
[ thread ]
[ subject ]
[ author ]
More information about the Python-list
mailing list