Neighbor-joining

Distance from the pair members to the new node

Taxa ${\displaystyle f}$ and ${\displaystyle g}$ are the paired taxa and ${\displaystyle u}$ is the newly created node. The branches joining ${\displaystyle f}$ and ${\displaystyle u}$ and ${\displaystyle g}$ and ${\displaystyle u}$, and their lengths, ${\displaystyle \delta (f,u)}$ and ${\displaystyle \delta (g,u)}$ are part of the tree which is gradually being created; they neither affect nor are affected by later neighbor-joining steps.