[boost] Re: Dimensional Analysis Interest?

From: Jan Langer (jan_at_[hidden])
Date: 2003-10-16 12:47:45

Brock Peabody wrote:
>>i think its really impossible, because you can't know what conversions
>>will be needed in a specific system. and if a user needs its own system
>>(like the gasoline thing beman mentioned), he needs to rewrite nearly
>>everything from scratch. the library can only provide some tools to
>>define dimensions and conversions and so on in a shorter way.
> 
> Ys, and I think it would be fairly straightforward assuming SI as base and
> some sort of compile time rational to specify conversion.  Straightforward
> for the user that is :)
> 
>   typedef rational<1,1> one;
> 
>   typedef measurement_system<rational<1000,1>,
>                              one,
>                              one,
>                              one,
>                              one,
>                              one,
>                              one,
>                              one>::type my_units;
> 
> 
> Where my_units would be the metric system except using kilograms instead of
> grams.

i think you confuse something here: quantities and units (maybe i am 
confusing the name ;-))
basically we need something like a dimension or unit represented as a 
type without any measuring stuff. in an abstract sense this should be 
like points in an n-dimensional space. the coordinates of this space are 
represented by some compile-time container of numbers (int or 
compile-time rational number or whatever).

now you define the operators for this space:
        addition between equal points
        multiplication -> addition of coordinates (exponents)

then a special system must be set up. eg the standard physical system. 
each unit (what is the real name of what i mean - length, mass, volume 
...) is just typedefed to a point in the space.

and the last layer defines quantities consisting of two compiletime 
values (actual value type and point in the exponent space) and a 
runtime-value.

what you try is to bring in the quantity in a too early layer.
jan

-- 
jan langer ... jan_at_[hidden]
"pi ist genau drei"