For a graph \(G=(V(G), E(G))\), a subset \(S \subset V(G)\) is a bipartite dominating set if every vertex in \(G-S\) is adjacent to a vertex in \(S\), and if the subgraph of \(G\) induced by \(S\) is bipartite. The bipartite domination number of \(G\), denoted by \(\gamma_{bip}(G)\), is the minimum cardinality of all bipartite dominating sets of \(G\). Xi and Yue [4] claimed that for every 2-connected outerplanar \(n\)-vertex graph \(G\), \(\gamma_{bip}(G) \leq \lceil \frac n 3 \rceil\), and that this bound is sharp. In this paper, correcting the result, we prove that \(\gamma_{bip}(G) \leq \lceil \frac 38 n \rceil\), where this bound is sharp.
Hartnell and Rall recently introduced the domatic number game. Alice and Bob color the vertices of a graph from a palette [\(k\)], and Alice wins if every color class is a dominating set at the end of the game. The largest winning palette size is denoted by \(\mathop{\mathrm{dom}}\nolimits_{g}(G)\) when Alice moves first and by \(\mathop{\mathrm{dom}}\nolimits'_{g}(G)\) when Bob moves first. Hartnell and Rall asked how these parameters behave under edge and vertex removal, and they also asked whether Bob can win with \(k\) colors while Alice wins with \(k+1\) colors. We give short answers. First, Alice-winning palettes are downward closed: if Alice can win with \(k+1\) colors, then she can win with \(k\) colors, in both versions of the game. Thus the proposed palette-size pathology never occurs. Second, if \(H\) is a spanning subgraph of \(G\), then \[ \mathop{\mathrm{dom}}\nolimits_{g}(H)\le \mathop{\mathrm{dom}}\nolimits_{g}(G),\qquad \mathop{\mathrm{dom}}\nolimits'_{g}(H)\le \mathop{\mathrm{dom}}\nolimits'_{g}(G). \] Thus edge deletion can never increase either invariant, and the inequalities may be strict. Finally, vertex deletion is not monotone: it can increase or decrease either invariant. Deleting one vertex can even increase either invariant by an arbitrarily large amount.
A graph \(G\) is said to be a an interval graph, if for each vertex \(u\) of \(G\), one can assign a set \(A_u\) which is a finite union of intervals on the real line such that \(u\) is adjacent to \(v\) in \(G\) if and only if \(A_u\cap A_v\neq\varnothing\). In this paper, we introduce a class of intersection graphs and show that it is equivalent to the class of interval graphs. We also investigate interval numbers of certain intersection graphs and establish several related results.
Motivated from the concept of strong regularity in the graph theory, few varieties of definitions for strongly regular signed graphs have been introduced. The initial one, which is due to Zaslavsky and the others are given by Stanic and Ramezani. The definition given by Stanic covers all the others. In this paper we provide some constructions for each of the definitions.
In this article, we obtain the determining number and the metric dimension of the zero-divisor graph of the ring of integers modulo \(n\) and of non-Boolean semisimple rings. For Boolean rings, an upper bound for these parameters is established. While the determining number and metric dimension of \(\Gamma(\mathbb{Z}_n)\) are known in the literature, we provide an alternative derivation based on a structural decomposition of the graph via generalized join. This approach offers a direct and unified method to compute these parameters. Further, we determine these parameters for joins of vertex-transitive graphs and investigate certain questions concerning the relationship between determining number and metric dimension.
Recently, Luo [3] introduced the Adding–Swapping Mapping Method to provide an alternative and constructive proof of Stanley’s [4] conjecture on perfect square permutations in \(S_n\) and asked whether the method extends to higher powers. In this paper we answer that question in a more limited but precise structural sense. For each fixed \(k\ge 2\), we define the \(k\)-signature \(R_k(w)\) recording the cycle-count vector modulo \(\gcd(m,k)\) in each length \(m\), and we prove a local residue transition law describing how the insertion map \(D_i\) updates the signature once the cycle length of the insertion point is specified. We also prove explicitly that every \(k\)-th power permutation has zero \(k\)-signature, so the signature gives a necessary obstruction to being a \(k\)-th power. This yields a residue-based partition of \(S_n\) that serves as an indexing scheme for insertion updates. We then show that for \(k\ge 3\) the insertion family does not preserve the class of \(k\)-th powers, explaining why the square case is exceptional from the standpoint of Luo’s method. Finally, we include explicit small-\(n\) data for \(k=3,4\) and prove that the density of \(k\)-th powers in \(S_n\) tends to \(0\) as \(n\to\infty\).
Let \(L(G(k))\) be a line graph of a \(k\)-subdivided graph \(G(k)\) of any connected, simple and undirected graph \(G\). In this paper, we fixed the valency dependence invariants of \(L(G(k))\) for \(k\geq2.\) Our results are the generalization of the results proved in [1,3,8].
This article studies edge irregular \((k)\)-labelings of complete graphs \((K_n)\) and aims to improve the existing upper bound for the edge irregularity strength \((es(K_n))\) through an algorithmic approach. The improvement is achieved using the branch and bound algorithm design strategy, whose selection is important because of the problem structure, computational complexity, possible serial or parallel execution, and accuracy requirements. Labeling complete graphs is difficult because the number of edges grows rapidly and many triangles are involved, making it challenging to maintain unique edge weights while searching for optimal labels. Since complete graphs serve as supergraphs for many graph families, results on them are particularly valuable. In 2018, Asim et al. proposed an algorithmic solution for complete graphs and gave the upper bound \((es(K_n)\leq E\log_2 |V|)\). This article uses the branch and bound strategy to address edge deficiency and improve that bound. Computational experiments are conducted for higher-order graphs, where the algorithm recursively generates constrained combinatorial structures to ensure unique edge weights. The results show that the proposed branch and bound algorithm significantly improves the upper bound for \((es(K_n))\) compared with previous results.
The exponential Randić index of a graph \(G\), denoted by \(ER(G)\), is defined as \(\sum\limits_{uv\in E(G)}e^{\frac{1}{d(u)d(v)}}\), where \(d(u)\) denotes the degree of a vertex \(u\) in \(G\). The line graph \(L(G)\) of a graph \(G\) is a graph in which each vertex represents an edge of \(G\), and two vertices are adjacent in \(L(G)\) if and only if their corresponding edges in \(G\) are incident to a common vertex. In this paper, we proved that for any tree \(T\) of order \(n\ge3\), \(ER(L(T))>\frac{n}{4}e^{\frac{1}{2}}\).
A strongly connected digraph \(D\) is primitive provided the greatest common divisor of the lengths of its directed cycles equals 1. The scrambling index of a primitive digraph \(D\) is the smallest positive integer \(k\) such that for every pair of vertices \(u\) and \(v\), there is a vertex \(w\) such that we can get to \(w\) from \(u\) and \(v\) in \(D\) by directed walks of length \(k\). In this paper, we characterize those primitive doubly symmetric digraphs with the largest scrambling index.
We prove the following necessary conditions for signed graphs on complete graphs to admit additive graceful labelings, thus considerably narrowing down the search for such labelings. If a signed graph on a complete graph \(K_p, ~p\not = 4\), with \(n\) negative and \(m\) positive edges, admits an additively graceful labeling, then (1) \(p\), \(p-2\) or \(p-4\) must be a perfect square, (2) If \(p\) is a perfect square then, both \(m\) and \(n\) are even, (3) If \(p-4\) is a perfect square then, both \(m\) and \(n\) are odd, (4) If \(p-2\) is a perfect square then, \(m\) and \(n\) have opposite parity and (5) The number of odd and even labeled vertices in \(S\) are \(\frac{p+\sqrt{p-i}}{2}\) and \(\frac{p-\sqrt{p-i}}{2}\) according as \(p-i\) is a perfect square, \(i=0,2\) or \(4\). We also provide an example to show that, if a signed graph \(S\) with no negative edges is additively graceful then, \(S\) as a graph need not be graceful. Interestingly, this example also settles 3 more open problems concerning gracefulness and edge consecutive gracefulness (ecg), thereby demonstrating that ecg or \(m\)-gracefulness is not a reliable measure of gracefulness.
We calculate several finite integrals involving trigonometric and hyperbolic functions by applying the Laplace convolution theorem and known inverse Laplace transform formulas. As a consequence, we obtain a new integral representation of the Kelvin function bei(z), and a new reduction formula for a particular generalized hypergeometric function. In addition, we present several new inverse Laplace transform formulas that do not appear to have been reported in the existing literature.
In this paper, we explore the enumerative combinatorics of American-style crossword puzzle grids under modified answer length requirements. While standard American-style crossword rules have a minimum answer length of three cells, we generalize this constraint to a minimum length \(m\) for an \(n\times n\) grid. We define \(\lvert Puz (n,m)\rvert\) as the number of such grids satisfying the standard structural rules of connectivity, \(180^\circ\) rotational symmetry, keyed squares, and full dimensionality. We prove that for \(m>\frac{n}{2}\), the number of valid grids is invariant under the transformation \(\lvert Puz (n,m)\rvert=\lvert Puz (n+1,m+1)\rvert\). Furthermore, we establish a closed-form formula for \(\lvert Puz (n,m)\rvert\) when \(m>\frac{n}{2}\). We also verify some counts for smaller grid dimensions verifying previously conjectured values.
Let \(G\) be a simple connected mixed graph, and let \(H(G)\) denote the Hermitian adjacency matrix of \(G\). The Hermitian permanental polynomial of \(G\) is defined as \(\pi(G; x) = \operatorname{per}(xI - H(G))\), where \(\operatorname{per}(\cdot)\) represents the permanent and \(I\) is the identity matrix. In this paper, we first derive fundamental properties of the Hermitian permanental polynomial for mixed graphs and establish explicit formulas relating its coefficients to those of the characteristic polynomial. We then analyze the root distribution of this polynomial, determining the number of zero roots for several special classes of mixed graphs. Finally, we characterize mixed graphs that remain cospectral under four‑way switching and prove that this operation preserves the permanental spectrum.
In finite desarguesian projective planes of prime power order \(q\), we consider the MDS codes obtained from ovals and generate new codes for the purpose of permutation decoding. We show that those new codes are \([q^2-1,3,(q-1)^2]_q\) codes and have \(s\)-PD-sets for \(s\le q-1\).
In this paper, we consider the relationship between toughness and the existence of \((g,f)\)-factors with inclusion/exclusion properties. We obtain that if \(t(G) \geq \frac{(a+b)^{2}+2(b-a)-3}{4(a+1)}\) with \(b > a \geq 2\) and \(a \leq g(x) < f(x) \leq b\) where \(a\), \(b\) are two integers, then for any two given edges \(e_{1}\) and \(e_{2}\), there exists a \((g,f)\)-factor including \(e_{1}\), \(e_{2}\); and a \((g,f)\)-factor including \(e_{1}\) and excluding \(e_{2}\); as well as a \((g,f)\)-factor excluding \(e_{1}\), \(e_{2}\).
A star edge coloring of a graph \(G\) is a proper edge coloring in which every path or cycle on four vertices contains at least three distinct colors. The star edge chromatic number of \(G\), denoted by \(\chi^\prime_{\mathrm{st}}(G)\), is the minimum number of colors required for such a coloring. In this paper, we study the star edge chromatic number of several graph classes derived from the Knödel graph \(W_{\Delta,n}\). In particular, we determine bounds and exact values for \(\chi^\prime_{\mathrm{st}}(G)\) for the Knödel graph \(W_{\Delta,n}\), its middle graph \(M\!\left(W_{\Delta,n}\right)\), and its Mycielskian \(\mu\!\left(W_{\Delta,n}\right)\). Furthermore, we provide explicit constructions of star edge colorings that attain these values.
The Euler Sombor (\(EU\)) index of a graph \(G\) is defined as \[EU(\mathit{G})=\sum \limits_{{\mathit{u}}{\mathit{v}}\in E(\mathit{G})} \sqrt{deg_G^2(u)+deg_G^2(v)+deg_G(u)deg_G(v)},\] where \(deg_G(u)\) and \(deg_G(v)\) are the degrees of the vertices \(u\) and \(v\) in the graph \(G\), respectively. Biswaranja Khanra and Shibsankar Das [Euler Sombor index of trees, unicyclic and chemical graphs, MATCH Commun. Math. Comput. Chem., 94 (2025) 525–548] posed an open problem to determine the extremal values and extremal graphs of the Euler Sombor index in the class of all connected graphs with a given domination number. In this paper, we solve this open problem for trees with a given domination number. Furthermore, we determine an upper bound for the Euler Sombor index of trees with a given independence number. We also characterize the corresponding extremal trees. Additionally, we propose a set of open problems for future research.
In 2003 W. Takahashi and M. Toyodaestablished the weak convergence of an iteration process to solve a variational inequality problem induced by an inverse strongly-monotone mapping. Recently we proved that for the same iterative process, most of its exact iterates are approximate solutions of the variational inequality. It was also shown that the iteration process for solving a variational inequality problem for an inverse strongly-monotone mapping generates approximate solutions in the presence of computational errors. In this work we employ the Cimmino algorithm in order to generalize these results for common approximate solutions of a finite family of variational inequalities with inverse strongly-monotone mappings and of a finite family of fixed point problems in the presence of computational errors.
Some equivalent statements and basic properties for the generalized convexity assumption p(x)f(x)+q(x)f '(x)+f ''(x)>= 0 are proved. Then based on these conclusions, various Jensen type inequalities under the generalized convexity are established. The idea is to transform such p(x),q(x)-convex functions to some simpler p(x), 0-convex or 0, q(x)-convex functions, or even convex functions. Ky Fan and Wang-Wang type inequalities are also generalized as applications.
