Editing Neighbor joining (section)

=== Conclusion: additive distances ===
This example represents an idealized case: note that if we move from any taxon to any other along the branches of the tree, and sum the lengths of the branches traversed, 
the result is equal to the distance between those taxa in the input distance matrix. For example, going from <math>d</math> to <math>b</math> we have <math>2+2+3+3=10</math>. A distance matrix whose distances agree in this way with some tree is said to be 'additive', a property which is rare in practice. Nonetheless it is important to note that, given an additive distance matrix as input, neighbor joining is guaranteed to find the tree whose distances between taxa agree with it.