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.