public static double cdf(double x,double mu,double sigma,double skew){
  x=(x - mu) / sigma;
  if (Math.abs(skew) > 0.) {
    double tmp=1 - skew * x;
    if (tmp < 1e-15) {
      return (skew < 0.) ? 0. : 1.;
    }
    x=-Math.log(tmp) / skew;
  }
  return .5 + .5 * NormalDistribution.erf(x * MathUtil.SQRTHALF);
}

public static double cdf ( double x , double mu , double sigma , double skew ) { x = ( x - mu ) / sigma ; if ( Math . abs ( skew ) > 0. ) { double tmp = 1 - skew * x ; if ( tmp < 1e-15 ) { return ( skew < 0. ) ? 0. : 1. ; } x = - Math . log ( tmp ) / skew ; } return .5 + .5 * NormalDistribution . erf ( x * MathUtil . SQRTHALF ) ; }
cumulative probability density function ( cdf ) of a normal distribution .
