As z Y V, the functions f ðzÞ ¼ e Àz and f ðzÞ ¼ logð1 þ e Àz Þ become increasingly similar, because log ð1 þ e Àz Þ Y e Àz as e Àz Y 0.
a second model then attempts to improve upon this initial ranking, using additional features of the tree as evidence.