anchor.diff:             (declare (type fixnum tree-id offset))
              (loop for i fixnum from 0 below len do
                (let ((leaf-index (node-leaf-index (find-leaf (dtree-root dtree) datamatrix i)))
  -                   (destination (svref refine-dataset i)))
  +                   (refine-datum (svref refine-dataset i)))
                  (declare (type fixnum leaf-index)
  -                        (type (simple-array fixnum) destination))
  -               (setf (aref destination tree-id) (+ leaf-index offset))))))
  +                        (type (simple-array fixnum) refine-datum))
  +               (setf (aref refine-datum tree-id) (+ leaf-index offset))))))
          (forest-dtree-list forest))
         refine-dataset)))
   
  
positive.code: (defstruct (forest (:constructor %make-forest)
                     (:print-object %print-forest))
    n-tree bagging-ratio datamatrix target dtree-list
    n-class class-count-array ; for classification
    datum-dim max-depth min-region-samples n-trial gain-test
    index-offset ; for global refinement
    )
  
  (defun %print-forest (obj stream)
    (if (forest-n-class obj)
  
negative.code:           do (setf (dtree-id dtree) i))
      ;; set leaf-id
      (set-leaf-index-forest! forest)
      (setf (forest-n-leaf forest)
            (apply #'+ (mapcar #'dtree-max-leaf-index
                               (forest-dtree-list forest))))
      forest))
  
  (defun make-regression-forest (datamatrix target
  