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Last update on 13. Nov 2025 .
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    NNI (Nearest Neighbour Interchange)

    DESCRIPTION

    Searches for a better (more parsimonious) tree by swapping the relative positions of subtrees separated by one edge. At each inner edge (i.e. at non-leaf edges) three different topologies are possible.

    Testing these 3 possible topologies and keeping the best of them, is called "Nearest Neighborhood Interchange" (NNI).

     

    Possible topologies tested by NNI

    The 3 different topologies checked by performing a NNI are

    (A,B,C = subtrees; R = rest of tree)

    R           R           R
 \           \           \
 /\          /\          /\
A  \        B  \        C  \
   /\          /\          /\
  B  C        A  C        B  A

    Note: there are no other possible topologies containing A,B,C and R!

     

    WARNINGS

    None

     

    BUGS

    No bugs known