Regular Graphs with Forbidden Subgraphs of $K_n$ with $k$ Edges

TL;DR

This paper investigates the minimum number of vertices in $d$-regular graphs with constraints on subgraph edges, motivated by distributed storage design, providing exact solutions for small $n$ and bounds for general cases.

Contribution

It introduces a new extremal graph problem related to fractional repetition codes and offers exact solutions for small $n$ with bounds for larger parameters.

Findings

Exact vertex counts for $3 \\leq n \\leq 5$

Bounds established for general $n$, $d$, and $k$

Extension of Turán-type extremal graph results

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 Tur\'an-type problem, are given. We present an almost complete solution for $3 \leq n \leq 5$.