question: public static double quantile ( double q , double [ ] x , int [ ] indices ) { if ( q < 0.0 || q > 1.0 ) throw new IllegalArgumentException ( "Quantile out of range" ) ; if ( q == 0.0 ) { return x [ indices [ 0 ] ] - 1.0 ; } return x [ indices [ ( int ) Math . ceil ( q * indices . length ) - 1 ] ] ; }
target:  compute the q-th quantile for a distribution of x (= inverse cdf)