$$Martin ratio = \frac{r_P - r_F}{\sqrt{\sum^{n}_{i=1} \frac{{D'_i}^2}{n}}}$$
where \(r_P\) is the annualized portfolio return, \(r_F\) is the risk free
rate, \(n\) is the number of observations of the entire series, \(D'_i\) is
the drawdown since previous peak in period i