Function returns the realized quad-power variation, defined in Andersen et al. (2012).
Assume there is \(N\) equispaced returns in period \(t\). Let \(r_{t,i}\) be a return (with \(i=1, \ldots,N\)) in period \(t\).
Then, the rQPVar is given by
$$
\mbox{rQPVar}_{t}=N*\frac{N}{N-3} \left(\frac{\pi^2}{4} \right)^{-4} \mbox({|r_{t,i}|} {|r_{t,i-1}|} {|r_{t,i-2}|} {|r_{t,i-3}|})
$$