public double pdf(double x){
  if (x <= 0.0)   throw new IllegalArgumentException();
  double logGamma=Fun.logGamma(freedom / 2.0);
  return Math.exp((freedom / 2.0 - 1.0) * Math.log(x / 2.0) - x / 2.0 - logGamma) / 2.0;
}

public double pdf ( double x ) { if ( x <= 0.0 ) throw new IllegalArgumentException ( ) ; double logGamma = Fun . logGamma ( freedom / 2.0 ) ; return Math . exp ( ( freedom / 2.0 - 1.0 ) * Math . log ( x / 2.0 ) - x / 2.0 - logGamma ) / 2.0 ; }
returns the probability distribution function .
