Re: Dimensional Analysis Interest? RV: [boost] Staticcompile-time fractions

From: Deane Yang (deane_yang_at_[hidden])
Date: 2003-10-22 14:41:05

I actually don't see why the different types of gasoline is too 
difficult to handle. I think a mistake is to assume that the dimensions
of the library must correspond to different physical dimensions.

I view the dimensions library as defining abstract dimensions, leaving 
it to the user or a higher level library to decide what they correspond 
to. One such higher level library would be the SIunits library.
But another user could define the dimensions to be volume of gasoline 
under different conditions.

What is true is that if the dimensions all correspond to volume of 
gasoline under diffferent conditions, the ability to generate arbitrary 
derived dimensions corresponding to products and ratios is less 
important. Still, one could imagine it to be useful to be able to 
represent the ratio of volume of gasoline at one temperature over the 
ratio of gasoline at another temperature.

What I might not have been clear enough so far is that I definitely
believe that the core library should be an essentially abstract 
mathematical library (just like <cmath>) that knows no physics
or chemistry. Then libraries with specific applications, like the 
SIunits library can be built on top of that.

I also believe that the typelists described by Hugo Duncan way back when
form a good basis on which to build this library.

Paul A. Bristow wrote:

> This was not unnoticed and definitely is of interest.  Suggest you should post
> your work so far, and examples of use, prefably annotated.
> 
> I note your use of rational dimensions to allow fractional (but not log and
> exp).
> 
> I'm inclined to agree that Beman's 'gas mix' problem may be too difficult to
> handle, for the reasons you give.
> 
> Paul
> 
> Paul A Bristow, Prizet Farmhouse, Kendal, Cumbria, LA8 8AB  UK
> [phone]   Mobile [phone]
> mailto:pbristow_at_[hidden]
> 
> 
> 
> -----Original Message-----
> From: boost-bounces_at_[hidden] [mailto:boost-bounces_at_[hidden]]On
> Behalf Of González Cuadrado, Miguel
> Sent: Monday, October 20, 2003 12:06 PM
> To: Boost mailing list
> Subject: [boost] Dimensional Analysis Interest? RV: [boost] Staticcompile-time
> fractions
> 
> This posting went apparently unnoticed, but it may be of interest to the
> "Dimensional Analysis" thread.
> <big snip>
> 
> By the way, IMHO the question about mixing gasoline is out of scope, since it is
> an altogether different problem, with very different semantics: fundamental
> dimensions are not multiplied as in dimensional analysis, but summed. It doesn't
> even support the same set of operations (no subtraction, semantics for
> multiplication is bscure, no division...).
> 
> 
> I have developed a small library that allows to do compile-time computations
> using rational numbers; it is heavily template-based. I use as a part of a units
> library (yet another), in which the dimension is encoded as seven rational
> numbers, one for the exponent of each of length, time, temperature and so on;
> each of these rational numbers is a template argument for a magnitude with
> dimension. (Fractional dimension units are used sometimes, for example for turbo
> engine analysis and simulation.
> 
> 
> 
> 
> 
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