question: public static double quantile ( double p , double alpha , double beta ) { if ( Double . isNaN ( alpha ) || Double . isNaN ( beta ) || Double . isNaN ( p ) || alpha < 0. || beta < 0. ) { return Double . NaN ; } if ( p < 0 || p > 1 ) { return Double . NaN ; } if ( p == 0 ) { return 0.0 ; } if ( p == 1 ) { return 1.0 ; } if ( p > 0.5 ) { return 1 - rawQuantile ( 1 - p , beta , alpha , logBeta ( beta , alpha ) ) ; } else { return rawQuantile ( p , alpha , beta , logBeta ( alpha , beta ) ) ; } }
target:  Compute quantile (inverse cdf) for Beta distributions.