Enumerating the total number of subtrees of trees

Abstract

Over some types of trees with a given number of vertices, which trees minimize or maximize the total number of subtrees or leaf containing subtrees are studied. Here are some of the main results:\ (1)\, Sharp upper bound on the total number of subtrees (resp. leaf containing subtrees) among $n$-vertex trees with a given matching number is determined; as a consequence, the $n$-vertex tree with domination number $\gamma$ maximizing the total number of subtrees (resp. leaf containing subtrees) is characterized. (2)\, Sharp lower bound on the total number of leaf containing subtrees among $n$-vertex trees with maximum degree at least $\Delta$ is determined; as a consequence the $n$-vertex tree with maximum degree at least $\Delta$ having a perfect matching minimizing the total number of subtrees (resp. leaf containing subtrees) is characterized. (3)\, Sharp upper (resp. lower) bound on the total number of leaf containing subtrees among the set of all $n$-vertex trees with $k$ leaves (resp. the set of all $n$-vertex trees of diameter $d$) is determined.