Re: 100%

From: René Scharfe <rene.scharfe@lsrfire.ath.cx>
Date: Jun 23, 2007, 11:41 UTC
Message-ID: <467D06D4.9050203@lsrfire.ath.cx>
In-Reply-To: <Pine.LNX.4.64.0706231154300.4059@racer.site>

Johannes Schindelin schrieb:

Show 23 quoted lines

> Hi,
> 
> On Sat, 23 Jun 2007, René Scharfe wrote:
> 
>> Johannes Schindelin schrieb:
>>> On Fri, 22 Jun 2007, David Kastrup wrote:
>>>> The people I know will expect "100% identical" or even "100.0% 
>>>> identical" to mean identical, period.  They will be quite surprised to 
>>>> hear that "99.95%" is supposed to be included.
>>> Granted, 100.0% means as close as you can get to "completely" with 4 
>>> digits. But if you have an integer, you better use the complete range, 
>>> rather than arbitrarily make one number more important than others.
>>>
>>> For if you see an integer, you usually assume a rounded value. If you 
>>> don't, you're hopeless.
>> Why hopeless?  It's a useful convention to define "100%" as "complete
>> (not rounded)".
> 
> By the same reasoning, you could say "never round down to 0%, because I 
> want to know when there is no similarity".
> 
> You cannot be exact when you have to cut off fractions, so why try for 
> _exactly_ one number?

Because completeness is special. If just one bit was available, I'd use it to indicate equality. That's what the authors of cmp(1) did, too. :)

And 0% is not special, at least not in a useful way that I can think of.
  I.e. there is no practical difference between "no two lines match" and
"one percent of the lines match".  If you're really interested in
similarities with an index below 10% then you'd better work with
absolute numbers instead of rounded percentages.

If someone came around with an interest in those cases with exactly 0% similarity, then we might need to decide between rounding up or down. But even in that hypothetical situation I think "equality" is still more interesting a data point than "really everything differs".

René