Re: Canonical DB
Date: Sat, 24 Jun 2006 10:58:36 +0200
> On Fri, 23 Jun 2006 21:59:52 +0200, "Dmitry A. Kazakov"
> <mailbox_at_dmitry-kazakov.de> wrote:
>>On Fri, 23 Jun 2006 15:37:54 +0200, 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.> distances if there are one-way routes involved.
> Why must it be symmetric? A to B and B to A may be different
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). 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.
-- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.deReceived on Sat Jun 24 2006 - 10:58:36 CEST