Tree Drifting
From TNT
Tree-drifting is quite similar to the ratchet, but the perturbation phase, instead of reweighting the characters, accepts the moves with a probability that depends on both the relative fit difference (Goloboff and Farris, 2001; see Goloboff, 1999) and the absolute fit difference between the tree being swapped and the new tree. It has the advantage that memory managing is easier, and for that reason is the only perturbator that sectorial-searches (see below) can use. The perturbation phase also alternates between acceptance of optimal trees only (O), and suboptimal trees (U): O,S,U,S,O,S,U… etc. Any of the O or U phases can be skipped (the O phase, with drift:noequal; or with the skip optimal-only drifting option in the tree-drift settings dialog box; the U becomes effectively an O by setting the score difference to a very low number).
Path: Analysis/New Technology search/Drift
