From: John Max Skaller (skaller_at_[hidden])
Date: 2001-06-22 17:38:52
> Would there be any interest in a small domain library for
> boost that handles dimensions (e.g. length, mass, power)
> and units (e.g. meters, feet, furlongs) of physical
> I would appreciate feedback on three main questions:
> 1) Is this appropriate for boost?
> 2) Has this already been done?
> 3) Does anyone see any fatal flaws in the general approach,
It looks good to me.
Some operations seems to be missing.
Suppose I write:
and x,y have units. What is the result?
A more pragmatic example is Pythagoras:
sqrt(x * x + y * y)
Here, x is in metres, so the argument to sqrt is
square metres, and the result should be in metres.
More generally, root(n,x) yields division
of the dimension by n (and an error if it isn't
integral -- unless you want to support fractal dimensions :-).
pow(x,n) yields multiplication of the unit by n.
So log(n,x) also yields division. (Guess?)
When it comes to trig functions ...
I guess I'm saying: dimensional correctness is a problematic
thing in physics, because all sorts of approximations
and kludges and special functions are used. At some stage,
you need to 'cast away' dimensions, do a pure computation,
then add the dimensions back.
sin ( undim(x) ) metres()
It would be kind of nice to wrap this up in a single
'cast away/cast back' operation (but I can't see how).
[A way to wrap existing 'pure' functions with dimensions?]
Is there a cast away function?
-- John (Max) Skaller, mailto:skaller_at_[hidden] 10/1 Toxteth Rd Glebe NSW 2037 Australia voice: 61-2-9660-0850 checkout Vyper http://Vyper.sourceforge.net download Interscript http://Interscript.sourceforge.net
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