Displaying 21 – 40 of 593

Showing per page

A modification of the median of a tree

Bohdan Zelinka (1993)

Mathematica Bohemica

The concept of median of a tree is modified, considering only distances from the terminal vertices instead of distances from all vertices.

A note on the cubical dimension of new classes of binary trees

Kamal Kabyl, Abdelhafid Berrachedi, Éric Sopena (2015)

Czechoslovak Mathematical Journal

The cubical dimension of a graph G is the smallest dimension of a hypercube into which G is embeddable as a subgraph. The conjecture of Havel (1984) claims that the cubical dimension of every balanced binary tree with 2 n vertices, n 1 , is n . The 2-rooted complete binary tree of depth n is obtained from two copies of the complete binary tree of depth n by adding an edge linking their respective roots. In this paper, we determine the cubical dimension of trees obtained by subdividing twice a 2-rooted...

A note on the independent domination number versus the domination number in bipartite graphs

Shaohui Wang, Bing Wei (2017)

Czechoslovak Mathematical Journal

Let γ ( G ) and i ( G ) be the domination number and the independent domination number of G , respectively. Rad and Volkmann posted a conjecture that i ( G ) / γ ( G ) Δ ( G ) / 2 for any graph G , where Δ ( G ) is its maximum degree (see N. J. Rad, L. Volkmann (2013)). In this work, we verify the conjecture for bipartite graphs. Several graph classes attaining the extremal bound and graphs containing odd cycles with the ratio larger than Δ ( G ) / 2 are provided as well.

A remark on branch weights in countable trees

Bohdan Zelinka (2004)

Mathematica Bohemica

Let T be a tree, let u be its vertex. The branch weight b ( u ) of u is the maximum number of vertices of a branch of T at u . The set of vertices u of T in which b ( u ) attains its minimum is the branch weight centroid B ( T ) of T . For finite trees the present author proved that B ( T ) coincides with the median of T , therefore it consists of one vertex or of two adjacent vertices. In this paper we show that for infinite countable trees the situation is quite different.

Currently displaying 21 – 40 of 593