spark-mllib gbdt algorithm questions
<p>has anyone read the mllib gbdt code? i have some questions about this algorithm, i don't know  how the program calculate the current node impurity, i only see the override calculate function in sub-class of Impurity ,in this function, parameter is sum of something, but where's the sum get from?  all the instances lable that belong to current node or child node should be added  first before call this function to get the sum value,but i haven't found.... Besides, if i want use another impurity method, what should i do? just modify the calculate(xx,xx,xx) function?</p>