question: private static double gnorm ( double a , double x ) { double sx ; if ( ( x <= 0.0 ) || ( a <= 0.0 ) ) { return 0.0 ; } else { sx = Math . sqrt ( a ) * 3.0 * ( Math . pow ( x / a , 1.0 / 3.0 ) + 1.0 / ( a * 9.0 ) - 1.0 ) ; return normalCdf ( sx ) ; } }
target:  Compute gamma cdf by a normal approximation