We observe recent results on the applications of extremal graph theory to cryptography. Classical Extremal Graph Theory contains Erdős Even Circuite Theorem and other remarkable results on the maximal size of graphs without certain cycles. Finite automaton is roughly a directed graph with labels on directed arrows. The most important advantage of Turing machine in comparison with finite automat...

symmetric division deg index is one of the 148 discrete adriatic indices that showed good predictive properties on the testing sets provided by international academy of mathematical chemistry.symmetric division deg index is defined by$$sdd(g) = sume left( frac{min{d_u,d_v}}{max{d_u,d_v}} + frac{max{d_u,d_v}}{min{d_u,d_v}} right),$$where $d_i$ is the degree of vertex $i$ in graph $g$.in this pap...

For a graph H $H$ , let c ( ) = inf { : e G ≥ | implies ≻ } $c(H)=\text{inf}\{c:e(G)\ge c|G|\,\,\text{implies}\,\,G\succ H\}$ where $G\succ H$ means that is minor of $G$ . We show if has average degree d $d$ then ≤ 0.319 … + o 1 log $c(H)\le (0.319\,\ldots \,+{o}_{d}(1))|H|\sqrt{\mathrm{log}d}$ $0.319\ldots $ an explicitly defined constant. This bound matches corresponding lower shown to hold f...

An upper bound on the saturation number for graphs as well as associated extremal graphs was given by (Kászonyi and Tuza in J. Graph Theory, 10:203–210, 1986). A minor improvement of that result, which was implied in their paper, will be stated. Using this result, a series of exact saturation numbers and associated extremal graphs will be proved for the nearly complete graphs Kt − E(L), where L...

Let G be a graph of order n with Laplacian spectrum μ1 ≥ μ2 ≥ · · · ≥ μn. The Laplacian-energy-like invariant of graph G, LEL for short, is defined as: LEL(G) = n−1 ∑ k=1 √ μk . In this note, the extremal (maximal and minimal) LEL among all the connected graphs with given matching number is determined. The corresponding extremal graphs are completely characterized with respect to LEL. Moreover ...

Using results from extremal graph theory, we determine the asymptotic number of string graphs with n vertices, i.e., graphs that can be obtained as the intersection graph of a system of continuous arcs in the plane. The number becomes much smaller, for any fixed d, if we restrict our attention to systems of arcs, any two of which cross at most d times. As an application, we estimate the number ...

Let U(n, g) and B(n, g) be the set of unicyclic graphs and bicyclic graphs on n vertices with girth g, respectively. Let B1(n, g) be the subclass of B(n, g) consisting of all bicyclic graphs with two edge-disjoint cycles and B2(n, g) = B(n, g)\B1(n, g). This paper determines the unique graph with the maximal signless Laplacian spectral radius among all graphs in U(n, g) and B(n, g), respectivel...

This paper is one of a series of papers in which, for a family L of graphs, we describe the typical structure of graphs not containing any L ∈ L. In this paper, we prove sharp results about the case L = {O6}, where O6 is the graph with 6 vertices and 12 edges, given by the edges of an octahedron. Among others, we prove the following results. (a) The vertex set of almost every O6-free graph can ...

Let G be a graph of order n with Laplacian spectrum μ1 ≥ μ2 ≥ · · · ≥ μn. The Laplacian-energy-like invariant of graph G, LEL for short, is defined as: LEL(G) = n−1 ∑ k=1 √ μk . In this note, the extremal (maximal and minimal) LEL among all the connected graphs with given matching number is determined. The corresponding extremal graphs are completely characterized with respect to LEL. Moreover ...