RE: [boost] Re: Date iterators in Boost Date-Time

From: Guillaume Melquiond (gmelquio_at_[hidden])
Date: 2003-08-18 02:35:43

En réponse à "Paul A. Bristow" <boost_at_[hidden]>:

> But as Michael Caine said "Not a lot of people know that" - so I trust
> you will explain what it does too for the benefit of us mere non-mathematical
> mortals!
> 
> Paul

I'm not sure to understand. Do you want me to explain what a convex hull is or
to explain what the function of the date-time library is supposed to do? I
suppose it's the first, since the second is what started this subthread.

A connected set is a set for which each couple of points are connected by a path
itself included in the set (all the points are reachable from all the points). A
convex set is a connected set with linear paths (all the points can be reached
from all the other points by following a segment). The convex hull of a set is
the smallest convex superset of it. For example, given three points in the
plane, the convex hull is the filled triangle defined by these points.

In the case of a 1-dimension space, connected and convex set are equals: they
are segments (or half-line or line or empty). Date manipulated by the date-time
library are in a 1-dimension space (the real line) and periods are segments
(non-empty bounded convex sets). So when you have two periods, the smallest
period enclosing these two is also the convex hull of them. Hence the name I
suggested.

I hope it makes sense.

Regards,

Guillaume