Re: Canonical DB
From: Dmitry A. Kazakov <mailbox_at_dmitry-kazakov.de>
Date: Sat, 24 Jun 2006 21:04:42 +0200
Message-ID: <12lniumjtzvb9$.1ceen1fyh0w2z.dlg_at_40tude.net>
>> Gene Wirchenko wrote:
>>
>> Rather when the space is anisotropic. If you just have many routes, you
>> still could get a metric distance by choosing the shortest path.
>>
>> ---------------
>> I found in Wikipedia that d(x,y) /= d(y,x) is called
>> quasimetric space (I never met such thing anywhere else).
>
> W = {Mon, Tue, Wed, Thu, Fri, Sat, Sun}
Date: Sat, 24 Jun 2006 21:04:42 +0200
Message-ID: <12lniumjtzvb9$.1ceen1fyh0w2z.dlg_at_40tude.net>
On Sat, 24 Jun 2006 13:02:42 +0200, mAsterdam wrote:
> 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}
That's a ring (modulo), which is not a metric space.
> d(Mon, Fri) = 4
> d(Fri, Mon) = 3
-- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.deReceived on Sat Jun 24 2006 - 21:04:42 CEST