Re: Canonical DB

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Sat, 24 Jun 2006 13:02:42 +0200
Message-ID: <449d1b74$0$31641$e4fe514c@news.xs4all.nl>

Dmitry A. Kazakov wrote:
> Gene Wirchenko wrote:

>> Dmitry A. Kazakov wrote:
>>> mAsterdam wrote:
>>
>>>> These requirements establish K as a clean point type.
>>>> Aside: With the last condition deleted one can make a
>>>> circular K, having distance(k1, k2) <> distance(k2, k1).
>>>
>>> That won't be formally a distance, which is required to be symmetric.
>>
>> Why must it be symmetric?  A to B and B to A may be different
>> distances if there are one-way routes involved.

>
> Rather when the space is anisotropic. If you just have many routes, you
> still could get a metric distance by choosing the shortest path.
>
> ---------------
> I found in Wikipedia that d(x,y) /= d(y,x) is called
> quasimetric space (I never met such thing anywhere else).

W = {Mon, Tue, Wed, Thu, Fri, Sat, Sun}

d(Mon, Fri) = 4
d(Fri, Mon) = 3

> Wikipedia also states that any
> quasimetric space can be made metric, by defining
>
> d*(x,y) = (d(x,y) + d(y,x)) / 2
>
> So it can be made metric.

Which is not always the sensible thing to do.

-- 
"The person who says it cannot be done
should not interrupt the person doing it."
Chinese Proverb.

Received on Sat Jun 24 2006 - 06:02:42 CDT