For each furcation in the tree, the relative difference between the distances of its subtrees is calculated.
'Distance' here is the sum of all branches between the furcation and the least distant leaf of the left resp. right subtree.
Relative difference Meaning
The nearer subtree has at least
of the farther subtrees distance.
Starting from the tree-tips, this function marks the more distant subtree of any furcation where the relative and absolute difference are above the specified minimas.
When a subtree has been marked, all further furcations between that subtree and the root of the whole tree will be ignored.
Poorly aligned sequences often result in long branches in the tree. Being able to identify those branches quickly helps to find those sequences.
The indented workflow is
search long branches
check alignment and data and fix any problems
recalculate tree parts (see ´Add species with local optimization´)
search again. Now you may find other branches, nearer to the tree root.