Re: [boost] Interest in dimension/unit-checking library?

From: Deane Yang (deane_yang_at_[hidden])
Date: 2005-10-12 20:30:26

Noah Stein wrote:
> I agree completely that we're talking about a 1-dimensional geometry.  I
> think the issue that people are arguing is, "What space are we using?"  For
> some, like you and Matt Calabrese, the answer is an affine space.
> Unfortunately, affine spaces don't directly support point combinations, so
> you create a function that has no meaning in your chosen space.
> 
> Others, such as I, view the natural geometry to be a Grassmann space which
> supports the addition and scalar weighting of points.  Addition of points is
> a natural and proper operation.  Unfortunately, the best discussion I've
> seen requires access to the ACM Digital Library:
> http://portal.acm.org/citation.cfm?id=504792 .
> 
(long discussion omitted)

This is a very cool idea for those who are willing to understand the 
geometry behind it all, but I suspect it's a little too mysterious for 
most users of the units library. Also, don't you need to store two 
numbers for each scalar quantity? Isn't that a little costly in both 
space and computation time? I think your approach makes more sense for 
points in more than one dimension, where storing n-dimensional points as 
(n+1)-vectors is less costly.

I don't really remember exactly what happened, but I think the last time 
we discussed this, I finally decided that it would be best to just 
implement a pure "vector quantity" library first. The "point quantity" 
interface could be added later, if a consensus develops. Otherwise, each 
of us can easily add our own layer on top of the vector quantity 
library. (So I'm retracting what I said in my post responding to Andy 
Little.)

I think this will provide a core library that will be useful to everyone.