<p>In <a href="https://github.com/mlpack/mlpack/pull/760#discussion_r74687398">src/mlpack/core/tree/hrectbound_impl.hpp</a>:</p>
<pre style='color:#555'>> }
>
> // Now take the Power'th root (but make sure our result is squared if it needs
> // to be); then cancel out the constant of 2 (which may have been squared now)
> // that was introduced earlier. The compiler should optimize out the if
> // statement entirely.
> - if (MetricType::TakeRoot)
> - return (ElemType) pow((double) sum, 1.0 / (double) MetricType::Power) / 2.0;
> + if (MetricType::Power == 1)
> + return sum * 0.5;
> + else if (MetricType::Power == 2)
> + {
> + if (MetricType::TakeRoot)
> + return std::sqrt(sum) * 0.5;
</pre>
<p>I believe the casts to double were done because <code>std::pow(double, int)</code> was not available on all systems. It looks like an overload of <code>std::sqrt()</code> is available that takes any integral type as input, but returns <code>double</code>, so you would have to cast the result back to <code>ElemType</code>. It appears that the same comments now apply about <code>std::pow</code> since C++11.</p>
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