We study partially distance-regular graphs and partially walkregular graphs as generalizations of distance-regular graphs and walkregular graphs respectively. We conclude that the partially distanceregular graphs can be viewed as some extremal graphs of partially walk-regular graphs. In the special case that the graph is assumed to be regular with four distinct eigenvalues, a well known class o...

For non-negative integers~$k$, we consider graphs in which every vertex has exactly $k$ vertices at distance~$2$, i.e., whose distance-$2$ are $k$-regular. We call such $k$-metamour-regular motivated by the terminology polyamory. While constructing is relatively easy -- provide a generic construction for arbitrary~$k$ finding all much more challenging. show that only with certain property canno...

Abstract Kim and Vu made the following conjecture ( Advances in Mathematics , 2004): if $$d\gg \log n$$ d≫logn then random d -regular graph $${\mathscr {G}}(n,d)$$ xmlns:mml="http://www.w3.org/1998/Math/MathML">G<...

We study a generalization of strongly regular graphs. We call a graph strongly walkregular if there is an ` > 1 such that the number of walks of length ` from a vertex to another vertex depends only on whether the two vertices are the same, adjacent, or not adjacent. We will show that a strongly walk-regular graph must be an empty graph, a complete graph, a strongly regular graph, a disjoint un...

Given a A:-regular graph G of order n, what is the minimum number v(G) of extra vertices required to embed G in a /<+1-regular graph? Clearly v(G) = 0 precisely when the complement G of G has a 1-factor—in particular, when n ^ 2k is even. Suppose G has no 1-factor: if n, k have opposite parity we show that v(G) = 1, while if n, k have the same parity (which must then be even with n < 2k) we sho...

Let Γ be a regular graph with n vertices, diameter D, and d + 1 different eigenvalues λ > λ1 > · · · > λd. In a previous paper, the authors showed that if P (λ) > n − 1, then D ≤ d − 1, where P is the polynomial of degree d−1 which takes alternating values±1 atλ1, . . . , λd. The graphs satisfying P (λ) = n − 1, called boundary graphs, have shown to deserve some attention because of their rich ...

‎a set $s$ of vertices of a graph $g=(v,e)$ without isolated vertex‎ ‎is a {em total dominating set} if every vertex of $v(g)$ is‎ ‎adjacent to some vertex in $s$‎. ‎the {em total domatic number} of‎ ‎a graph $g$ is the maximum number of total dominating sets into‎ ‎which the vertex set of $g$ can be partitioned‎. ‎we show that the‎ ‎total domatic number of a random $r$-regular graph is almost‎...