## Author ORCID Identifier

https://orcid.org/0000-0003-1790-2804

## Date of Award

5-2-2022

## Degree Type

Dissertation

## Degree Name

Doctor of Philosophy (PhD)

## Department

Mathematics and Statistics

## First Advisor

Hein van der Holst

## Second Advisor

Marina Arav

## Third Advisor

Guantao Chen

## Fourth Advisor

Frank J. Hall

## Fifth Advisor

Zhongshan Li

## Abstract

A signed graph is an ordered pair (*G*,Σ), where *G* = (*V*, *E*) is a graph and Σ ⊆ *E*. The edges in Σ are called odd, and the edges in *E* \ Σ are called even. The family of matrices *S*(*G*,Σ) is defined such that if [*a _{i}*

_{,}

*] =*

_{j}*A*∈

*S*(

*G*,Σ), then

*a*

_{i,j}< 0 if there is at least one edge between

*i*and

*j*and if all edges between

*i*and

*j*are even;

*a*

_{i,j}> 0 if there is at least one edge between

*i*and

*j*and if all edges between

*i*and

*j*are odd;

*a*

_{i,j}∈

**R**if there is at least one even edge and at least one odd edge between

*i*and

*j*; and

*a*

_{i,j}= 0 if there are no edges between

*i*and

*j*. The maximum nullity of a signed graph

*M*(

*G*,Σ) is the largest corank(

*A*) for

*A*∈

*S*(

*G*, Σ). The matrix

*A*∈

*S*(

*G*, Σ) has the Strong Arnold Property with respect to (

*G*,Σ) if

*X*= 0 is the only matrix such that

*AX*= 0, and

*x*

_{i,j }= 0 if

*i*is adjacent to

*j*or

*i*=

*j*. The stable maximum nullity of a signed graph ξ(

*G*,Σ) is the largest corank(

*A*) for

*A*∈

*S*(

*G*,Σ) where

*A*has the Strong Arnold Property. Here, we present a combinatorial characterization of signed graphs with maximum nullity at most two, extending a result of Johnson, Loewy, and Smith. We also find the forbidden minors for signed graphs with stable maximum nullity at most two, extending a result of Hogben and van der Holst. We generalize the notion of zero forcing to signed graphs. We find the zero forcing number of signed graphs with maximum nullity at most two, extending a result of Row.

## DOI

https://doi.org/10.57709/28777057

## Recommended Citation

Dahlgren, Fredrick S., "Signed Graphs with Maximum Nullity at Most Two." Dissertation, Georgia State University, 2022.

doi: https://doi.org/10.57709/28777057

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