From: John Maddock (john_at_[hidden])
Date: 2008-02-05 11:56:54
Martin Bonner wrote:
>> The only use case I can think of is where the argument is an integer
>> rather than a real number (and the result is therefore a double),
>
> boost.units:
> pow<3>( length )
> is going to have units of volume.
Ah yes, forgot that. My gut feeling is that Boost.Math should concentrate
on the um... math: provide a nice simple implementation that's reasonably
efficient too. And libraries like Boost.Units can overload it for
dimentioned-quantities, and use the Boost.Math version for the internal
calculation. Does this make sense?
> ... and I /believe/ that boost.units only needs half powers. So
> (modulu units)
>
> template<class T1, class T2, int N>
> T2 pow<N,2>(T1 val) { return sqrt(pow<N>(val)); }
>
> should do it.
>
> ... in fact, I suspect that boost.math pow should /only/ offer the
> integral powers, and boost.units should wrap it to add the rational
> support.
I guess the question is can we evaluate half-powers more efficiently than
just using pow? Maybe, but it's not so obvious to me as it is for smallish
integer powers.
John.