public double pdf(double x){
  double diff=x - mean;
  return SQRT_INV * Math.exp(-(diff * diff) / (2.0 * variance));
}

public double pdf ( double x ) { double diff = x - mean ; return SQRT_INV * Math . exp ( - ( diff * diff ) / ( 2.0 * variance ) ) ; }
returns the probability distribution function .
