Questions tagged [trees]

A tree is a connected graph without cycles, with a finite or infinite number of vertices. There are many variants of trees, according to further constraints or decorations.

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73 views

Probability process involving blocking paths of rooted tree

Consider a rooted tree $T$ and $n$ leaf nodes which are all at depth $R$. We would like to select a random subset $S$ of the edges of $T$, such that (i) Every root-leaf path of $T$ contains at least ...
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123 views

Finding a tree with adjacency matrix near a given matrix

For defining a distance between trees, one can code them into $\mathbb{R}^n$ and use norms in $\mathbb{R}^n$ as distance. (For example we can use adjacency matrices as a tool for this coding) After ...
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Parity of oriented rooted trees

Suppose we have a planar graf with vertices $v_o, \ldots, v_n$, where $n$ is even such that if we checkerboard-color regions in the complement, then the black regions are $n$ (non-degenerated) ...
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Can I express this random variable in terms of known distributions?

By computing the Laplace transform of the total length of a random tree (the nested Kingman coalescent tree with coalescence rates $\gamma$ for the individuals and $\gamma'$ for the species), we would ...
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145 views

Trees and spans of edge labels

Let $T$ be a rooted tree with $m$ leaves. Label every edge with a label of the form $x_i$ or $-x_i$, for some letter $x_i$. For each leaf in the tree, consider the formal linear combination $v$ ...
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Grassmannian cluster algebra of infinite type has no trees in its mutation class

The question is why the statement in the title is true (is it?). To elaborate, recall that Grassmannian cluster algebra, according to Scott`s paper Grassmannians and Cluster Algebras, is the cluster ...
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60 views

(Weakly) connected sets with large (out-)boundary

Let $\Gamma=(V,E)$ be a connected undirected graph with n vertices such that every vertex has degree at least $4$. Now draw arrows on some of the edges, in such a way that the in-degree of every ...
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Tree property at weak inaccessibles

Suppose $\kappa$ is a weakly inaccessible cardinal with the tree property. What can we say about the height of $\kappa$? Is it a weakly-hyper-Mahlo of some sort? Does it enjoy some kind of ...
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113 views

Decomposing a metric tree as a union of rooted (or “centered”) trees

Suppose $G$ is a finite metric tree whose set of leaves is $A=\{v_1, \ldots, v_n\}$. Consider the function $G\to \mathbb R_+$ that assigns to a point $x$ the distance from $x$ to $A$, denoted $d(x, A)$...
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Gromov hyperbolicity constant vs. Gromov-Hausdorff distance to a tree

Let $X$ be a compact, geodesic metric space which is Gromov hyperbolic with a constant $\delta>0$. To fix scaling, let us also assume that $X$ has diameter $1$. To fix a definition of Gromov ...
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1answer
78 views

Smallest size of graph covered by infinite tree

Let $T$ be the universal covering tree of some finite, connected, non-tree graph, and let $n_0(T)$ be the smallest positive integer such that there exists a graph $G$ (loops and multiple edges allowed)...
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Is the Frog game solvable in the root of a full binary tree?

This is a cross-post from math.stackexchange.com$^{[1]}$, since the bounty there didn't lead to any new insights. For reference, The Frog game is the generalization of the Frog Jumping (see it on ...
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265 views

How does the number of trees on $n$ vertices *up to isomorphism* grow as $n \to \infty$?

It is well known that the number of labelled trees on $n$ vertices is equal to $n^{n-2}$. We do not expect any such exact formula for the number of isomorphism types of trees on $n$ vertices. But ...
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Relation between Kirchhoff's Circuital law and Matrix tree Theorem

I'm not a professional mathematician, just an undergraduate student. I was reading Introduction to Graph Theory by West, I came over the topic which discuses the methods to find the spanning trees in ...
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Chromatic number of square of a tree

What is an upper bound on the chromatic number of the square of a tree on $n$ vertices? Note that the power of the graph is considered in this sense. If the tree were a path, then it is easy to see ...
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Are all intermediate growth branch groups just-infinite?

Are all branch groups of intermediate growth just-infinite? I can't seem to find an answer to this one way or another; the question is motivated by the fact all examples of intermediate growth branch ...
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43 views

Counting number of special subset of vertices in a tree

As defined in this article, an ordered pair $ (X,Y) $ of disjoint subsets of the vertices of a graph $ G $ with $ \vert X \vert = \vert Y \vert =2 $, is called an odd pair if the number of edges with ...
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501 views

A tree with prime vertices

Let us construct a simple (undirected) graph $T$ as follows: $\quad$ Let the set of all primes be the vertex set of $T$. For each prime $p$, take the least prime $q>p$ such that $2(p+1)-q$ is ...
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Is there a name for a tree with all leaf vertices identified with each other?

Is there a name for those graphs that can be formed by taking a tree and identifying all the vertices of degree 1 (leaves) with each other? Or, if I understand correctly, an equivalent definition may ...
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1answer
130 views

What do you call a set of vertices that separates the root from the leaves?

Suppose we are given a rooted tree $T$, and a set of vertices $M$ that separates the root of $T$ from its leaves. In other words, every path from the root of $T$ to a leaf contains a vertex in $M$. Is ...
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Bound on the number of unlabeled tree on n vertices

By the Cayley's Theorem, the number of labeled tree on n vertices is at most n^{n-2}. On the other hand, what is the bound on the number of unlabeled tree on n vertices?
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Algorithm to generate free unlabelled trees uniformly at random

I am implementing an algorithm to generate free unlabelled trees uniformly at random (uar). For this I found this paper by Herbert S. Wilf (The uniform selection of trees. 1981. In Journal of ...
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Infinite trees whose spectrum has more than 3 connected components

I was wondering whether there exists any infinite tree $T$ such that the action of $\mathit{Aut}(T)$ on the set of vertices $V=V(T)$ has finitely many orbits, and whose spectrum $\sigma(T)$ has ...
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150 views

mapping integers to k-ary trees

Is there an algorithmic way to map the natural numbers to unique k-ary trees? I am familiar with the work of Tychonievich who created a mapping from integers to binary trees. https://www.cs.virginia....
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Examples of non-uniform lattices in products of trees

Consider a product of two locally-finite, infinite, unimodular trees $X=T_1\times T_2$. Assume that both ${\rm Aut}(T_1)$ and ${\rm Aut}(T_2)$ are not discrete. So as a vague general question, what ...
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364 views

Number of tree walks of bounded degree

Define a tree walk to be a walk $w$ on some tree starting and ending at the origin. Its support $\text{supp}(w)$ is the subtree consisting of the vertices and edges it traverses. Define the maximal ...
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71 views

Existence of limit computable map

Is there a limit computable function $\Phi$ with the following properties? Let $T\subset \mathbb{N}^{<\mathbb{N}}$ be a tree (coded as its characteristic function) and $f\in\mathbb{N}^\mathbb{N}$ ...
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1answer
120 views

Sign-reversing involution proof of tree inversion generating function at $-1$ equals number of alternating permutations?

For a labeled tree $T$ on $\{1,2,...,n\}$ an inversion of $T$ is a pair $1 < i < j \leq n$ such that $j$ belongs to the unique path from $1$ to $i$ (we think of $T$ as being rooted at $1$). Let $...
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Finite index subgroup of HNN extension

Let $GX$ be a tree group (a right-angled Artin group such that the graph is a tree), such that not all the subgroups of $GX$ are necessarily RAAGs, so the length of the tree is greater or equal than $...
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1answer
227 views

Gromov-Hausdorff distance between weighted tree graphs

I would like to measure the similarity between a pair of weighted tree graphs. According to this post, this can be done by regarding the trees as metric spaces and then applying the Gromov-Hausdorff ...
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268 views

Compactly generated vertex stabilisers in compactly generated t.d.l.c. groups acting on trees

In the article cited below, I. Castellano gives a proof for the following result (Proposition 4.1). Let $G$ be a compactly generated totally disconnected locally compact group. Suppose that $G$ ...
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Infimums of Poset of Unlabelled Subtrees

I will use $T$ to refer to the set of unlabelled, rooted trees, and use $(t,r)$ to denote a tree and its root. Let $(T, \preceq)$ be a poset where $(t_1,r_1) \preceq (t_2,r_2)$ means that $t_1$ is a ...
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1answer
238 views

Quotient graph of a tree

We know that every graph is isomorphic to a subgraph of a complete graph. Similarly, can we say that every graph is isomorphic to a quotient graph of a tree?
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166 views

Reference request on a bijection on trees related to Narayana numbers

The following bijection on rooted plane trees arises in the following context : the counting sequence of (rooted plane) trees with $n$ edges ($n+1$ vertices) and $k$ leaves is given by: $$\frac{1}{n} ...
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Is there a way to generate a graph of specified treewidth

The treewidth is a parameter of the graph that describes its similarity to a tree. Treewidth is NP-hard to find. For the introduction please see wikipedia The question is how to generate interesting ...
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102 views

Distinct sums for edge weights

For each $n\geq1$, consider a special tree with $2n+1$ nodes which are assigned values $a_i$ from the set $\{0,0,1,2,3,\dots,2n-1\}$. Only $0$ can be a repeated assignment. The edges are only the ones ...
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Does a bounded branching/log depth dihotomy hold for rooted trees?

Let $T$ be a rooted tree. For any subtree $T' \subset T$ write $L(T')$ for the number of leaves of $T'$. Further, for $T' \subset T$ define the branch-depth of a node $v \in T'$ as the number of ...
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894 views

Groups acting on trees

Assume that $X$ is a tree such that every vertex has infinite degree, and a discrete group $G$ acts on this tree properly (with finite stabilizers) and transitively. Is it true that $G$ contains a ...
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Treewidth problem equivalence

Say we are solving a tree decomposition problem, e.g. given a graph $G = (V, E)$ we try to find a chordal graph $H$ such that $V(H) = V(G)$, $E(G) \in E(H)$ and the maximal clique in $H$ is minimal ...
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Admissible (unitary) spherical representation $sl(2,Q_p)$. Does dimension fixed point vector increase proportional index

I am using terminology of Cartier's Harmonic analysis on trees. Take $\pi$ be one of the irreducible principal or complementary (unitary) spehrical series of $Sl(2, Q_p)$. Let $K$ be the maximal ...
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Terminology about trees

In set theory, a tree is usually defined as a partial order such that the set of elements below any given one is well-ordered. I am interested in the class of partial orders $P$ such that for every $...
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Distributions of “sequential” binomials

I have come across the following stochastic process which seems very elementary, although I do not know any appropriate terminology for it; I greatly appreciate any suggestions! Suppose I am given ...
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1answer
530 views

Destroying Suslin, nothing special

Recall that a tree on $\omega_1$ is called Suslin if every chain and antichain are countable. If every level is countable and there are no cofinal branches, then it is called Aronszajn (in particular ...
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Typical labelled vs. unlabelled trees properties

Consider two random tree models $T_1(n)$ and $T_2(n)$, chosen equiprobably among labelled and unlabelled trees on $n$ vertices respectively. I'm wondering if there are properties that are vastly more ...
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Almost graceful tree conjecture

The graceful tree conjecture is the following statement: for any tree $T = (V, E)$ with $|V| = n$ there is a bijective map $f: V \to [n]$ such that $D = \{|f(x) - f(y)| \mid xy \in E\} = [n - 1]$. ...
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1answer
293 views

A monad that unions sets

Suppose we have a monad that maps types of some kind to other types (see below) , and let types be sets. Let $\alpha, \beta$ be types, $\rightarrow$ denote a function between types, and let $a : \...
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Are there Prüfer sequences for rooted forests?

One well-known, extremely slick proof of Cayley's tree enumeration theorem is the use of Prüfer sequences. Cayley also proved a version for forests, namely that the number of forests with $n$ ...
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173 views

Two disjoint trees

Let $G$ be a graph and let $A_1, A_2 \subseteq V(G)$ be disjoint sets of vertices. Let us call $(A_1, A_2)$ independent if there exist vertex-disjoint trees $T_1, T_2 \subseteq G$ within $G$ which ...
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Partitioning the vertices of a graph into induced trees

I am looking for previous work regarding graphs whose vertices can be assigned colours (not necessarily a proper colouring) in such a way that each colour class induces a tree. In particular I am ...
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The number of Laplacian eigenvalues of a graph in interval [k,n]

There are several upper and lower bounds for $m_G[2,n]$ (the number of Laplacian eigenvalues of a graph $G$ with $n$ vertices in the interval $[2,n]$). I want to know whether there exists any bound ...