code: public void plus(LinearSparseVector sv, float w) {
  		if (sv == null)
  			return;
  		for (int i = 0; i < sv.length; i++) {
  			float val = (float) sv.data[i] * w;
  			add(sv.index[i], val);
  		}
  	}
docs: 计算x+y*w
  
  @param sv
  @param w