Diversity (mathematics)

In mathematics, a diversity is a generalization of the concept of metric space.

The concept was introduced in 2012 by Bryant and Tupper,[1] who call diversities "a form of multi-way metric".

[2] The concept finds application in nonlinear analysis.

[3] Given a set

fin

be the set of finite subsets of

A diversity is a pair

consisting of a set

satisfying

δ (

δ (

Bryant and Tupper observe that these axioms imply monotonicity; that is, if

They state that the term "diversity" comes from the appearance of a special case of their definition in work on phylogenetic and ecological diversities.

They give the following examples: Let

be a metric space.

defines a diversity.

For all finite

if we define

If T is a phylogenetic tree with taxon set X.

For each finite

, define

as the length of the smallest subtree of T connecting taxa in A.

is a (phylogenetic) diversity.

be a metric space.

For each finite

denote the minimum length of a Steiner tree within X connecting elements in A.

define

is defined for any finite A as the largest clique of A, then

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