Regular graphs with forbidden subgraphs of K<SUB align="right">n with k edges

Abstract

In this paper we raise a variant of a classic problem in extremal graph theory, which is motivated by a design of fractional repetition codes, a model in distributed storage systems. For any feasible positive integers $d\geq 3$, $n \geq 3$, and $k$, where $n-1 \leq k \leq \binom{n}{2}$, what is the minimum possible number of vertices in a $d$-regular undirected graph whose subgraphs with $n$ vertices contain at most $k$ edges? The goal of this paper is to give the exact number of vertices for each instance of the problem and also to provide some bounds for general values of $n$, $d$, and $k$. A few general bounds with some exact values, for this Turan-type problem, are given. We present an almost complete solution for $3 \leq n \leq 5$.