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Johan Kok

Publications and source records attributed to Johan Kok.

59 records · Page 4Linked to original sources

A note on $f^\pm$-Zagreb indices in respect of Jaco Graphs, $J_n(1), n \in \Bbb N$ and the introduction of Khazamula irregularity

The topological indices $irr(G)$ related to the \emph{first Zagreb index,} $M_1(G)$ and the \emph{second Zagreb index,} $M_2(G)$ are the oldest irregularity measures researched. Alberton $[3]$ introduced the \emph{irregularity} of $G$ as $irr(G) = \sum\limits_{e \in E(G)}imb(e), imb(e) = |d(v) - d(u)|_{e=vu}$. In the paper of Fath-Tabar $[7]$, Alberton's indice was named the \emph{third Zagreb indice} to conform with the terminology of chemical graph theory. Recently Ado et.al. $[1]$ introduced the topological indice called \emph{total irregularity}. The latter could be called the \emph{fourth Zagreb indice}. we define the $\pm$\emph{Fibonacci weight,} $f^\pm_i$ of a vertex $v_i$ to be $-f_{d(v_i)},$ if $d(v_i)$ is uneven and $f_{d(v_i)}$, if $d(v_i)$ is even. From the aforesaid we define the $f^\pm$-Zagreb indices. This paper presents introductory results for the undirected underlying graphs of Jaco Graphs, $J_n(1), n \leq 12$. For more on Jaco Graphs $J_n(1)$ see $[9, 10]$. Finally we introduce the \emph{Khazamula irregularity} as a new topological variant.

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The Derivative Degree Sequences of Finite Simple Connected Graphs are Parking Functions

Parking functions are well researched and interesting results are found in the listed references and more. Some introductory results stemming from application to degree sequences of simple connected graphs are provided in this paper. Amongst others, the result namely, that a derivative degree sequence, $d_d(G) \in \Bbb D_d(G)= \{(\lceil\frac{d(v_1}{\ell}\rceil, \lceil\frac{d(v_2)}{\ell}\rceil, \lceil\frac{d(v_3)}{\ell}\rceil, ..., \lceil\frac{d(v_n)}{\ell}\rceil| \ell = d(v_i), \forall i,$ with $d(v_i)\geq 2\},$ of a simple connected graph $G$ is a parking function, is presented. We also introduce the concept of \emph{looping degree sequences} and the \emph{looping number}, $ξ(G)$. Four open problems are proposed as well.

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A note on the number of edges of the Jaco Graph, $J_n(1), n \in \Bbb N

Kok et.al. [3] introduced Jaco Graphs \emph{(order 1)}. It is hoped that as a special case, a closed formula can be found for the number of edges of a finite Jaco Graph $J_n(1)$. However, the algorithms discussed in Ahlbach et.al. [1] suggest this might not be possible. Finding a closed formula for the number of edges of a Jaco Graph $J_n(1), n \in \Bbb N$ remains an interesting open problem. In this note we present three alternative, \emph{formula}.

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Characteristics of Jaco Graphs, $J_\infty(a), a \in \Bbb N$

We introduce the concept of a family of finite directed graphs (order a) which are directed graphs derived from an infinite directed graph (order a), called the a-root digraph. The a-root digraph has four fundamental properties which are; $V(J_\infty(a)) = \{v_i|i \in \Bbb N\}$ and, if $v_j$ is the head of an edge (arc) then the tail is always a vertex $v_i, i n.$ Hence, trivially we have $d(v_i) \leq ai$ for $i \in \Bbb N.$ We present an interesting Lucassian-Zeckendorf result and other general results of interest. It is meant to be an introductory paper to encourage exploratory research.

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Characteristics of Finite Jaco Graphs, $J_n(1), n \in \Bbb N$

We introduce the concept of a family of finite directed graphs (order 1) which are directed graphs derived from an infinite directed graph (order 1), called the 1-root digraph. The 1-root digraph has four fundamental properties which are; $V(J_\infty(1)) = \{v_i|i \in \Bbb N\}$ and, if $v_j$ is the head of an edge (arc) then the tail is always a vertex $v_i, i n.$ Hence, trivially we have $d(v_i) \leq i$ for $i \in \Bbb N$. We present an interesting Fibonaccian-Zeckendorf result and present the Fisher Algorithm to table particular values of interest. It is meant to be an introductory paper to encourage exploratory research.

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