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From: Daniel Frey (daniel.frey_at_[hidden])
Date: 20040105 07:31:43
Alan Bellingham wrote:
> Daniel Frey:
>
>
>>Wait! I think the above mixes up some important concepts. Look at this:
>>
>>length <> meter
>>time <> hour
>>speed <> mph
>>frequency <> hertz
>>
>>I hope you see what I mean. 'hertz' is IMHO totally different than
>>length, time or speed.
>
>
> Only in that frequency is the inverse of period  and is therefore a
> 1/time unit.
>
> length <> meter
> time <> second
> speed <> meters/second
> frequency <> /second
>
> When you're doing dimensional analysis, you may multiply a length by a
> frequency to get a speed  for example, the wavelength of a particular
> radio band times its frequency should give you the speed of light.
Of course, but that's not a contradiction of what I said above. It just
shows that there is more to a unitlibrary like relationship. To make
this clear:
speed = length/time
(which you can't use that way directly, as C++types don't work that
way) and
mph = mile/hour
The former can probably be written like this:
typedef divide< length, time >::type speed;
But I have to admit that I haven't put enough thinking into units so
far. I'd like to finish the constant libraries first (I'm working on the
documentation) before having a closer look at units. As I said already,
I think that meter, second and hertz are constants, so I think that
there is also a connection between the two fields...
Regards, Daniel
 Daniel Frey aixigo AG  financial solutions & technology SchloßRaheStraße 15, 52072 Aachen, Germany fon: +49 (0)241 93673742, fax: +49 (0)241 93673799 eMail: daniel.frey_at_[hidden], web: http://www.aixigo.de
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