# Induced Subgraphs in Strongly Regular Graphs

## TL;DR

This thesis develops algorithms and theoretical tools to analyze the counts of induced subgraphs in strongly regular graphs, especially triangle-free ones, with applications to open problems and automorphism insights.

## Contribution

It introduces a linear equation-based algorithm for induced subgraph counts and applies it to a famous open SRG case, providing new bounds and automorphism insights.

## Key findings

- Number of induced subgraphs depends on Petersen graph counts in SRG(3250,57,0,1)
- Bounds established for induced $K_{3,3}$ in triangle-free SRGs
- Automorphism insights for specific SRGs

## Abstract

This thesis focuses on theoretical and algorithmic tools for determining the numbers of induced subgraphs in strongly regular graphs, SRGs, and on further applications of such numbers. We consider in more detail a restricted class of these graphs, specifically those with no triangles. In this special case, there are infinitely many feasible sets of parameters for SRGs. Despite this fact there are only seven known examples of such graphs. we develop an algorithm which produces linear equations describing various relations between numbers of induced subgraphs of orders $o$ and $o-1$ in a SRG. We apply our results also on $srg(3250,57,0,1)$ (existence of which is a famous open problem). In this case, the number of induced subgraphs isomorphic to a given graph on $10$ vertices depends only on the number of induced Petersen graphs. Furthermore, we provide new insights about automorphisms of $srg(3250,57,0,1)$ as well as bounds for the numbers of induced $K_{3,3}$ in general triangle-free SRGs. At the end of the thesis we discuss possible extension of our approach for the study of so called $t$-vertex condition.