Re: [boost] Re: Physical Quantities revisited

From: Rene Jager (renej_at_[hidden])
Date: 2003-10-25 17:41:07

> On 2003-10-24, Deane Yang <deane_yang_at_[hidden]> wrote:
>>  I can't disagree with that, but from listening to the physicists
>> explain
>>  their needs, I haven't heard anything that the physicists want that
>>  isn't also wanted by many of us non-physicists, except the desire to
>>  hardwire the definition of dimensions to actual physical dimensions. So
>>  all I am trying to express is the desire not to have the core library
>>  somehow tied to physical dimensions only.
>
> Why not start with what we know is wanted, and develop from that?
>
> There is clearly a desire for a library which supports
> physical dimensions - if at a later point other things are required,
> then a bit of refactoring will allow the physical dimension
> library to built on the more generic core (if it ever exists).
> Much like boost::shared_ptr may, or may not, ever build on a
> policy based smart pointer.
>
>>  Angles are indeed difficult to fit within the framework of a
>>  dimensions/units library. The basic problem is that an angle is really
>> a
>>  unitless ratio. [...]
>
> Ahem.  Angles have *lots* of units - degrees, radians, gradians ...
> they don't, however, have any "dimensionality".
>
> It is an important, if pedantic, distinction.

Although dimensionless, angle and solid angle are something special and
there should be some support for them; for example, making it optional to
treat them as additional base quantities.
With respect to SI they are refered to as "supplementary SI quantities"
(supplementary base units radian and steradian).

renej

>
> phil
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