symNodesI | R Documentation |

This function calculates the symmetry nodes index `SNI(T)`

for a given rooted
binary tree `T`

. `SNI(T)`

is defined as the number of inner vertices `v`

that are not
symmetry nodes, i.e. the two pending subtrees rooted at the children of `v`

do not
have the same tree shape.

For `n=1`

the function returns `SNI(T)=0`

and a warning.

For details on the symmetry nodes index, see
also Chapter 18 in "Tree balance indices: a comprehensive survey" (https://doi.org/10.1007/978-3-031-39800-1_18).

```
symNodesI(tree)
```

`tree` |
A rooted binary tree in phylo format. |

`symNodesI`

returns the symmetry nodes index of the given tree.

Sophie Kersting

S. J. Kersting, M. Fischer. Measuring tree balance using symmetry nodes — A new balance index and its extremal properties. Mathematical Biosciences, page 108690, 2021. ISSN 0025-5564. doi:https://doi.org/10.1016/j.mbs.2021.108690

```
tree <- ape::read.tree(text="((((,),),(,)),(((,),),(,)));")
symNodesI(tree)
```

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