Editing Distance matrix (section)

== Ultrametric distance matrix ==
The ultrametric distance matrix is defined as  an additive matrix which models the constant [[molecular clock]]. It is used to build a phylogenetic tree. A matrix {{mvar|M}} is said to be ultrametric  if there exists a tree {{mvar|T}} such that:

* {{mvar|M{{sub|ij}}}} equals the sum of the edge weights along the path from {{mvar|i}} to {{mvar|j}} in {{mvar|T}}
* A root of the tree can be identified  with the distance to all the leaves being the same

Here is an example of an ultrametric distance matrix with its corresponding tree:

[[File:Ultrametric tree.png|frameless|395x395px|center]]