public static double pchisq(double x){
  double xh=Math.sqrt(x);
  return pnorm(xh) - pnorm(-xh);
}

public static double pchisq ( double x ) { double xh = Math . sqrt ( x ) ; return pnorm ( xh ) - pnorm ( - xh ) ; }
returns the cumulative probability of the chi - squared distribution
