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From: Paul A. Bristow (boost_at_[hidden])
Date: 2003-08-18 17:24:44

Thanks - it does now make sense, but since (mercifully!) time is only
1-dimensional, I find the span suggestion more intuitive.


PS This explanation could usefully be added to the interval library
documentation. I was puzzled why the word 'hull' was used.

| -----Original Message-----
| From: boost-bounces_at_[hidden]
| [mailto:boost-bounces_at_[hidden]]On Behalf Of Guillaume Melquiond
| Sent: Monday, August 18, 2003 8:36 AM
| To: Boost mailing list
| Subject: RE: [boost] Re: Date iterators in Boost Date-Time
| 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


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