question: @ Override public double calculateDistance ( double [ ] x1 , double [ ] x2 ) { double norm2 = norm2 ( x1 , x2 ) ; double exp1 = sigma1 == 0.0d ? 0.0d : Math . exp ( ( - 1 ) * norm2 / sigma1 ) ; double exp2 = sigma2 == 0.0d ? 0.0d : Math . exp ( ( - 1 ) * norm2 / sigma2 ) ; double exp3 = sigma3 == 0.0d ? 0.0d : Math . exp ( ( - 1 ) * norm2 / sigma3 ) ; return exp1 + exp2 - exp3 ; }
target:  Calculates kernel value of vectors x and y. 