question: public static double cdf ( double val , double mu , double sigma , double k ) { final double x = ( val - mu ) / sigma ; if ( k > 0 || k < 0 ) { if ( k * x > 1 ) { return k > 0 ? 1 : 0 ; } return Math . exp ( - Math . exp ( Math . log ( 1 - k * x ) / k ) ) ; } else { return Math . exp ( - Math . exp ( - x ) ) ; } }
target:  CDF of GEV distribution