From: Calamitas <calamitates@...>
Date: 2007-09-03T19:29:08+09:00
Subject: Re: Bug in % (Float)?

On 03/09/07, Morton Goldberg <m_goldberg@ameritech.net> wrote:
> On Sep 2, 2007, at 7:57 PM, Calamitas wrote:
> > Well, the smallest n for which m_mod_n(1.0, 1.0 / n) is way off is n =
> > 93. If it's any consolation though, among the first million n, there
> > are only 78161 for which m_mod_n doesn't give something zeroish. There
> > are 497886 such n for which Ruby's built-in % is off.
>
> That is a real consolation :)
>
> Seriously, to me, this is the most convincing argument you've come up
> with in support of your position that finding a better method for
> computing % with floats is a lost cause.

In theory, I think it's possible to do % in a way that enforces that
1.0 % (1.0 / n) equals 0.0 or something close to it. This could be
done by shifting the discontinuity slightly. But it creates a bias
that may be detrimental to other applications.

> > Will you let me know what Wolfram Research answers?
>
> Certainly. I'll pass it on directly to your gmail account. It may be
> some time before I get an answer since they are a bit swamped right
> now with problems arising from their new Mathematica 6 release, and
> my query is a minor side-issue from their POV.

Ok, thanks.

Regards,
Peter