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Our main result is a sharp bound for the number of vertices in a minimal forbidden subgraph for the graphs having minimum rank at most 3 over the finite field of order 2. We also list all 62 such minimal forbidden subgraphs. We conclude by exploring how some of these results over the finite field of order 2 extend to arbitrary fields and demonstrate that at least one third of the 62 are minimal forbidden subgraphs over an arbitrary field for the class of graphs having minimum rank at most 3 in that field.
A emph{sign pattern (matrix)} is a matrix whose entries are from the set ${+, -, 0}$. The emph{minimum rank} (respectively, emph{rational minimum rank}) of a sign pattern matrix $cal A$ is the minimum of the ranks of the real (respectively, rational)
The zero forcing number Z(G), which is the minimum number of vertices in a zero forcing set of a graph G, is used to study the maximum nullity / minimum rank of the family of symmetric matrices described by G. It is shown that for a connected graph o
A sign pattern matrix is a matrix whose entries are from the set ${+,-,0}$. If $A$ is an $mtimes n$ sign pattern matrix, the qualitative class of $A$, denoted $Q(A)$, is the set of all real $mtimes n$ matrices $B=[b_{i,j}]$ with $b_{i,j}$ positive (r
Given three nonnegative integers $p,q,r$ and a finite field $F$, how many Hankel matrices $left( x_{i+j}right) _{0leq ileq p, 0leq jleq q}$ over $F$ have rank $leq r$ ? This question is classical, and the answer ($q^{2r}$ when $rleqminleft{ p,qright}
In Martin Gardners October, 1976 Mathematical Games column in Scientific American, he posed the following problem: What is the smallest number of [queens] you can put on a board of side n such that no [queen] can be added without creating three in a