Square-root velocity function
= Square-root velocity function
{title2=$Q(f)$}
For an absolutely continuous real function $f$, its square-root velocity function is $Q(f)=f'/\sqrt{|f'|}$ where $f'\ne0$, with value zero where $f'=0$. Under an increasing reparameterization $\gamma$, it transforms as $Q(f\circ\gamma)=(Q(f)\circ\gamma)\sqrt{\gamma'}$.