We consider a ring \(R_{u^3} = \mathbb{F}_2+u\mathbb{F}_2+u^2\mathbb{F}_2+u^3\mathbb{F}_2, u^4=0\). We discuss the structure of self-dual codes, Type I codes and Type II codes over the ring \(R_{u^3}\) in terms of the structure of their Torsion and Residue codes. We construct Type I and Type II optimal codes over the ring \(R_{u^3}\) for different lengths.

Magic squares are known to mankind since ages. With their eye catching properties, they have attracted and inspired researchers to further explore and work with them. The present paper is written with an aim to explore the usefulness of magic squares in the construction of partially balanced incomplete block (PBIB) designs. In this regard, we have proposed a new method for the construction of magic squares and studied their properties. We have also established a link between these properties and some existing association schemes. We have then introduced four new association schemes using these properties which have been later used for the construction of PBIB designs.

We consider a vertex-coloring problem where the amount one pays for using a color is a function of how many times the color is used. For a cost-function \(f\), we define the \(f\)-chromatic number of graph \(G\) as the minimum cost of a (proper) coloring of \(G\), and focus on the case that the marginal costs \(f(i+1)-f(i)\) are non-increasing. We provide bounds for general graphs, for specific classes of graphs, and for some operations on graphs. We also consider the number of colors used in an optimal coloring, and for example, characterize the trees where the bipartite coloring is not always optimal.

Let \(q\) be a positive integral power of some prime \(p\) and \(\mathbb{F}_{q^m}\) be a finite field with \(q^m\) elements for some \(m \in \mathbb{N}\). Here we establish a sufficient condition for the existence of primitive normal pairs of the type \((\epsilon, f(\epsilon))\) in \(\mathbb{F}_{q^m}\) over \(\mathbb{F}_{q}\) with two prescribed traces, \(\text{Tr}_{{\mathbb{F}_{q^m}}/{\mathbb{F}_q}}(\epsilon)=a\) and \(\text{Tr}_{{\mathbb{F}_{q^m}}/{\mathbb{F}_q}}(f(\epsilon))=b\), where \(f(x) \in \mathbb{F}_{q^m}(x)\) is a rational function with some restrictions and \(a, b \in \mathbb{F}^*_q\). Furthermore, for \(q=5^k\), \(m \geq 9\) and rational functions with degree sum 4, we explicitly find at most 13 fields in which the desired pair may not exist.

Let \(G = (V(G), E(G))\) be a simple connected graph. The inverse sum indeg index of \(G\), denoted by \(\text{ISI}(G)\), is defined as the sum of the weights \(\frac{d(u)d(v)}{d(u) + d(v)}\) of all edges \(uv\) of \(G\), where \(d(u)\) denotes the degree of a vertex in \(G\). In this paper, we first present some lower and upper bound for \(ISI\) index in terms of graph parameters such as maximum degree, minimum degree and clique number. Moreover, we compute \(ISI\) index of several graph operations like join, cartesian product, composition, corona and strong product of graphs.

We consider the eternal distance-2 domination problem, recently proposed by Cox, Meger, and Messinger, on trees. We show that finding a minimum eternal distance-2 dominating set of a tree is linear time in the order of the graph by providing a fast algorithm. Additionally, we characterize trees that have eternal distance-2 domination number equal to their domination number or their distance-2 domination number, {along with trees that are} eternal distance-2 domination critical. We conclude by providing general upper and lower bounds for the eternal distance-k domination number of a graph. We construct an infinite family of trees which meet said upper bound and another infinite family of trees whose eternal distance-k domination number is within a factor of 2 of the given lower bound.

We apply the splitting operation defined on binary matroids (Raghunathan et al., 1998) to \(p\)– matroids, where \(p\)-matroids refer to matroids representable over \(GF(p).\) We also characterize circuits, bases, and independent sets of the resulting matroid. Sufficient conditions to yield Eulerian \(p\)-matroids from Eulerian and non-Eulerian \(p\)-matroids by applying the splitting operation are obtained. A class of connected \(p\)-matroids that gives connected \(p\)-matroids under the splitting operation is characterized. In Application, we characterize a class of paving \(p\)-matroids, which produces paving matroids after the splitting operation.

For a connected graph \(G=(V,E)\) of order at least two, a \(u-v\) chordless path in \(G\) is a \(monophonic\) \(path\). The edge monophonic closed interval \(I_{em}[u,v]\) consists of all the edges lying on some \(u-v\) monophonic path. For \(S'\subseteq V(G),\) the set \(I_{em}[S']\) is the union of all sets \(I_{em}[u,v]\) for \(u,v\in S'.\) A set \(S'\) of vertices in \(G\) is called an \(edge\) \(monophonic\) \(set\) of \(G\) if \(I_{em}[S']=E(G).\) The edge monophonic number \({m_1}(G)\) of G is the minimum cardinality of its edge monophonic sets of \(G\). In this paper the monophonic number and the edge monophonic number of corona product graphs are obtained. Exact values are determined for several classes of corona product graphs.