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Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Lights Out on Related Graphs

Laura Ballard

Hope College REU withErica Budge and Dr. Darin Stephenson

Summer 2012

October 16, 2015

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 1 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

What is “Lights Out”?

The original Tiger Electronics game:

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 2 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

What is “Lights Out”?

The original Tiger Electronics game:

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 3 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

What is “Lights Out”?

Each light is a vertex

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 4 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

What is “Lights Out”?

Connections are edges

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 5 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

What is “Lights Out”?

In the Z2 case, 1 is “on” and 0 is “o↵”

Blankverticesare instate 0.

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 6 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

What is “Lights Out”?

In the Z2 case, 1 is “on” and 0 is “o↵”

Blankverticesare instate 0.

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 6 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

What is “Lights Out”?

The finished product:

1 1

1 1 1

1 1

1

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 7 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

What is “Lights Out”?

Another graph:

1

1 1

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 8 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

What is “Lights Out”?

Definition

A press on a vertex v increases the state of v and all adjacentvertices by 1.

In Z2,1 + 1 = 0.

1

1 1

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 9 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

What is “Lights Out”?

Definition

A press on a vertex v increases the state of v and all adjacentvertices by 1.

In Z2,1 + 1 = 0.

1

1 1

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 9 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

What is “Lights Out”?

Definition

A press on a vertex v increases the state of v and all adjacentvertices by 1.

In Z2,1 + 1 = 0.

1 1

1 1

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 10 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

What is “Lights Out”?

Definition

A press on a vertex v increases the state of v and all adjacentvertices by 1.

In Z2,1 + 1 = 0.

1 1

1 1

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 11 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

What is “Lights Out”?

Definition

A press on a vertex v increases the state of v and all adjacentvertices by 1.

In Z2,1 + 1 = 0.

1

1 1

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 12 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

What is “Lights Out”?

Remember, the objective is to turn all of the lights out.

1

1 1

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 13 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

What is “Lights Out”?

Lights out!!

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 14 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

It gets better!

But we don’t just work in Z2...

In Zk , possible states are between 0 and k � 1.

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 15 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

It gets better!

But we don’t just work in Z2...In Zk , possible states are between 0 and k � 1.

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 15 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

In Z4:

But we don’t just work in Z2...In Zk , possible states are between 0 and k � 1.

3

2

3 1

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 16 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

In Z4:

3

2

3 1

In Z4,3 + 1 = 0.

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 17 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

In Z4:

3

2

3 1

In Z4,3 + 1 = 0.

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 17 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

In Z4:

1

3

3 1

In Z4,3 + 1 = 0.

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 18 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

For multiple presses:

A pattern is a vector that represents multiple presses on agraph G .

For example, pattern ~y would press A twice and everyother vertex once:

A

B C D

E

~y =

0

BBBB@

21111

1

CCCCA

ABCDE

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 19 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

For multiple presses:

A pattern is a vector that represents multiple presses on agraph G .

For example, pattern ~y would press A twice and everyother vertex once:

A

B C D

E

~y =

0

BBBB@

21111

1

CCCCA

ABCDE

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 19 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

For multiple presses:

A pattern is a vector that represents multiple presses on agraph G .

For example, pattern ~y would press A twice and everyother vertex once:

A

B C D

E

~y =

0

BBBB@

21111

1

CCCCA

ABCDE

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 19 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

For multiple presses:

A pattern is a vector that represents multiple presses on agraph G .

For example, pattern ~y would press A twice and everyother vertex once:

A

B C D

E

~y =

0

BBBB@

21111

1

CCCCA

ABCDE

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 19 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Definition

If a state can be turned all o↵ by applying a pattern, that stateis a winnable state.

B C

A

1

D

1

E F

1

0

BBBBBB@

100101

1

CCCCCCA

ABCDEF

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 20 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Definition

If a state can be turned all o↵ by applying a pattern, that stateis a winnable state.

B C

A

1

D

1

E F

1

0

BBBBBB@

100101

1

CCCCCCA

ABCDEF

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 20 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Definition

If a state can be turned all o↵ by applying a pattern, that stateis a winnable state.

B C

A1

D1

E F1

0

BBBBBB@

100101

1

CCCCCCA

ABCDEF

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 20 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Definition

If a state can be turned all o↵ by applying a pattern, that stateis a winnable state.

B C

A1

D1

E F1

0

BBBBBB@

100101

1

CCCCCCA

ABCDEF

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 20 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Definition

If a state can be turned all o↵ by applying a pattern, that stateis a winnable state.

B C

A1

D1

E F1

0

BBBBBB@

100101

1

CCCCCCA

ABCDEF

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 20 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Linear Algebra

A

B C D

E

G

Neighborhood Matrix of G(denoted N(G ))

A B C D EA 1 1 1 1 0B 1 1 1 0 1C 1 1 1 1 1D 1 0 1 1 1E 0 1 1 1 1

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 21 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Linear Algebra

A

B C D

E

G

Neighborhood Matrix of G(denoted N(G ))

A B C D EA 1 1 1 1 0B 1 1 1 0 1C 1 1 1 1 1D 1 0 1 1 1E 0 1 1 1 1

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 21 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Linear Algebra

A

B C D

E

G

Neighborhood Matrix of G(denoted N(G ))

A B C D EA

1 1 1 1 0

B

1 1 1 0 1

C

1 1 1 1 1

D

1 0 1 1 1

E

0 1 1 1 1

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 21 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Linear Algebra

A

B C D

E

G

Neighborhood Matrix of G(denoted N(G ))

A B C D EA

1

1 1 1

0

B 1

1

1

0

1C 1 1

1

1 1D 1

0

1

1

1E

0

1 1 1

1

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 21 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Linear Algebra

A

B C D

E

G

Neighborhood Matrix of G(denoted N(G ))

A B C D EA

1

1 1 1 0B 1

1

1 0 1C 1 1

1

1 1D 1 0 1

1

1E 0 1 1 1

1

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 21 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Linear Algebra

A

B C D

E

G

Neighborhood Matrix of G(denoted N(G ))

A B C D EA 1 1 1 1 0B 1 1 1 0 1C 1 1 1 1 1D 1 0 1 1 1E 0 1 1 1 1

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 21 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Linear Algebra

A

B C D

E

G

Neighborhood Matrix of G(denoted N(G ))

0

BBBB@

1 1 1 1 01 1 1 0 11 1 1 1 11 0 1 1 10 1 1 1 1

1

CCCCA

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 22 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Linear Algebra

The “initial state” of a graph can also be represented as avector ~x .

2

A

0

B

1

C

2

D

2

E

In Z3:~x =

0

BBBB@

20122

1

CCCCA

ABCDE

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 23 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Linear Algebra

The “initial state” of a graph can also be represented as avector ~x .

2A

0B

1C

2D

2E

In Z3:

~x =

0

BBBB@

20122

1

CCCCA

ABCDE

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 23 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Linear Algebra

The “initial state” of a graph can also be represented as avector ~x .

2A

0B

1C

2D

2E

In Z3:~x =

0

BBBB@

20122

1

CCCCA

ABCDE

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 23 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Applying Patterns

N~y gives the e↵ect of applying pattern ~y to graph G .

N~y =

0

BBBB@

1 1 1 1 01 1 1 0 11 1 1 1 11 0 1 1 10 1 1 1 1

1

CCCCA

0

BBBB@

21111

1

CCCCA=

2

0

BBBB@

11110

1

CCCCA+ 1

0

BBBB@

11101

1

CCCCA+ 1

0

BBBB@

11111

1

CCCCA+ 1

0

BBBB@

10111

1

CCCCA+ 1

0

BBBB@

01111

1

CCCCA

=

0

BBBB@

21211

1

CCCCA

}Pressing A

Pressing vertices in a pattern is commutative.

For every pattern ~y , N~y 2 CSk(G )

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 24 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Applying Patterns

N~y gives the e↵ect of applying pattern ~y to graph G .

N~y =

0

BBBB@

1 1 1 1 01 1 1 0 11 1 1 1 11 0 1 1 10 1 1 1 1

1

CCCCA

0

BBBB@

21111

1

CCCCA=

2

0

BBBB@

11110

1

CCCCA+ 1

0

BBBB@

11101

1

CCCCA+ 1

0

BBBB@

11111

1

CCCCA+ 1

0

BBBB@

10111

1

CCCCA+ 1

0

BBBB@

01111

1

CCCCA

=

0

BBBB@

21211

1

CCCCA

}Pressing A

Pressing vertices in a pattern is commutative.

For every pattern ~y , N~y 2 CSk(G )

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 24 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Applying Patterns

N~y gives the e↵ect of applying pattern ~y to graph G .

N~y =

0

BBBB@

1 1 1 1 01 1 1 0 11 1 1 1 11 0 1 1 10 1 1 1 1

1

CCCCA

0

BBBB@

21111

1

CCCCA=

2

0

BBBB@

11110

1

CCCCA+ 1

0

BBBB@

11101

1

CCCCA+ 1

0

BBBB@

11111

1

CCCCA+ 1

0

BBBB@

10111

1

CCCCA+ 1

0

BBBB@

01111

1

CCCCA

=

0

BBBB@

21211

1

CCCCA}Pressing A

Pressing vertices in a pattern is commutative.

For every pattern ~y , N~y 2 CSk(G )

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 24 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Applying Patterns

N~y gives the e↵ect of applying pattern ~y to graph G .

N~y =

0

BBBB@

1 1 1 1 01 1 1 0 11 1 1 1 11 0 1 1 10 1 1 1 1

1

CCCCA

0

BBBB@

21111

1

CCCCA=

2

0

BBBB@

11110

1

CCCCA+ 1

0

BBBB@

11101

1

CCCCA+ 1

0

BBBB@

11111

1

CCCCA+ 1

0

BBBB@

10111

1

CCCCA+ 1

0

BBBB@

01111

1

CCCCA

=

0

BBBB@

21211

1

CCCCA

}Pressing A

Pressing vertices in a pattern is commutative.

For every pattern ~y , N~y 2 CSk(G )

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 24 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Applying Patterns

N~y gives the e↵ect of applying pattern ~y to graph G .

N~y =

0

BBBB@

1 1 1 1 01 1 1 0 11 1 1 1 11 0 1 1 10 1 1 1 1

1

CCCCA

0

BBBB@

21111

1

CCCCA=

2

0

BBBB@

11110

1

CCCCA+ 1

0

BBBB@

11101

1

CCCCA+ 1

0

BBBB@

11111

1

CCCCA+ 1

0

BBBB@

10111

1

CCCCA+ 1

0

BBBB@

01111

1

CCCCA

=

0

BBBB@

21211

1

CCCCA

}Pressing A

Pressing vertices in a pattern is commutative.

For every pattern ~y , N~y 2 CSk(G )

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 24 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Applying Patterns

N~y gives the e↵ect of applying pattern ~y to graph G .

N~y =

0

BBBB@

1 1 1 1 01 1 1 0 11 1 1 1 11 0 1 1 10 1 1 1 1

1

CCCCA

0

BBBB@

21111

1

CCCCA=

2

0

BBBB@

11110

1

CCCCA+ 1

0

BBBB@

11101

1

CCCCA+ 1

0

BBBB@

11111

1

CCCCA+ 1

0

BBBB@

10111

1

CCCCA+ 1

0

BBBB@

01111

1

CCCCA

=

0

BBBB@

21211

1

CCCCA

}Pressing A

Pressing vertices in a pattern is commutative.

For every pattern ~y , N~y 2 CSk(G )

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 24 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Applying Patterns

N~y gives the e↵ect of applying pattern ~y to graph G .

N~y =

0

BBBB@

1 1 1 1 01 1 1 0 11 1 1 1 11 0 1 1 10 1 1 1 1

1

CCCCA

0

BBBB@

21111

1

CCCCA=

2

0

BBBB@

11110

1

CCCCA+ 1

0

BBBB@

11101

1

CCCCA+ 1

0

BBBB@

11111

1

CCCCA+ 1

0

BBBB@

10111

1

CCCCA+ 1

0

BBBB@

01111

1

CCCCA=

0

BBBB@

21211

1

CCCCA}Pressing A

Pressing vertices in a pattern is commutative.

For every pattern ~y , N~y 2 CSk(G )

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 24 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Applying Patterns

The new state of G after pattern ~y is complete is N~y + ~x .

0

BBBB@

21211

1

CCCCA+

0

BBBB@

20122

1

CCCCA=

0

BBBB@

41333

1

CCCCAmod 3 =

0

BBBB@

11000

1

CCCCA

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 25 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Applying Patterns

The new state of G after pattern ~y is complete is N~y + ~x .

0

BBBB@

21211

1

CCCCA+

0

BBBB@

20122

1

CCCCA=

0

BBBB@

41333

1

CCCCAmod 3 =

0

BBBB@

11000

1

CCCCA

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 25 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Applying Patterns

The new state of G after pattern ~y is complete is N~y + ~x .

0

BBBB@

21211

1

CCCCA+

0

BBBB@

20122

1

CCCCA=

0

BBBB@

41333

1

CCCCAmod 3

=

0

BBBB@

11000

1

CCCCA

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 25 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Applying Patterns

The new state of G after pattern ~y is complete is N~y + ~x .

0

BBBB@

21211

1

CCCCA+

0

BBBB@

20122

1

CCCCA=

0

BBBB@

41333

1

CCCCAmod 3 =

0

BBBB@

11000

1

CCCCA

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 25 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

When we apply patterns, the goal is to change each vertex tostate 0:

N~y + ~x = ~0

N~y = �~x

~y = N�1 ⇤ (�~x)

If N is invertible mod k , every initial state ~x is winnable, andN�1 ⇤ (�~x) is the winning pattern.

Graphs for which N is invertible mod k are called always

winnable mod k .

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 26 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

When we apply patterns, the goal is to change each vertex tostate 0:

N~y + ~x = ~0

N~y = �~x

~y = N�1 ⇤ (�~x)

If N is invertible mod k , every initial state ~x is winnable, andN�1 ⇤ (�~x) is the winning pattern.

Graphs for which N is invertible mod k are called always

winnable mod k .

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 26 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

When we apply patterns, the goal is to change each vertex tostate 0:

N~y + ~x = ~0

N~y = �~x

~y = N�1 ⇤ (�~x)

If N is invertible mod k , every initial state ~x is winnable, andN�1 ⇤ (�~x) is the winning pattern.

Graphs for which N is invertible mod k are called always

winnable mod k .

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L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

When we apply patterns, the goal is to change each vertex tostate 0:

N~y + ~x = ~0

N~y = �~x

~y = N�1 ⇤ (�~x)

If N is invertible mod k , every initial state ~x is winnable, andN�1 ⇤ (�~x) is the winning pattern.

Graphs for which N is invertible mod k are called always

winnable mod k .

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Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

When we apply patterns, the goal is to change each vertex tostate 0:

N~y + ~x = ~0

N~y = �~x

~y = N�1 ⇤ (�~x)

If N is invertible mod k , every initial state ~x is winnable, andN�1 ⇤ (�~x) is the winning pattern.

Graphs for which N is invertible mod k are called always

winnable mod k .

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Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

When we apply patterns, the goal is to change each vertex tostate 0:

N~y + ~x = ~0

N~y = �~x

~y = N�1 ⇤ (�~x)

If N is invertible mod k , every initial state ~x is winnable, andN�1 ⇤ (�~x) is the winning pattern.

Graphs for which N is invertible mod k are called always

winnable mod k .

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Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Remember that N~y 2 CSk(G ).

N~y = �~x is solvable if ~x is winnable.

Thus, ~x is winnable if and only if ~x 2 CSk(G ).

(Null Space of G - NSk(G ))

Since N is a symmetric matrix, NSk(G ) is the orthogonalcomplement of CSk(G ).

A graph is always winnable mod k if and only ifdimNSk(G ) = 0.

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ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Remember that N~y 2 CSk(G ).

N~y = �~x is solvable if ~x is winnable.

Thus, ~x is winnable if and only if ~x 2 CSk(G ).

(Null Space of G - NSk(G ))

Since N is a symmetric matrix, NSk(G ) is the orthogonalcomplement of CSk(G ).

A graph is always winnable mod k if and only ifdimNSk(G ) = 0.

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Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Remember that N~y 2 CSk(G ).

N~y = �~x is solvable if ~x is winnable.

Thus, ~x is winnable if and only if ~x 2 CSk(G ).

(Null Space of G - NSk(G ))

Since N is a symmetric matrix, NSk(G ) is the orthogonalcomplement of CSk(G ).

A graph is always winnable mod k if and only ifdimNSk(G ) = 0.

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Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Remember that N~y 2 CSk(G ).

N~y = �~x is solvable if ~x is winnable.

Thus, ~x is winnable if and only if ~x 2 CSk(G ).

(Null Space of G - NSk(G ))

Since N is a symmetric matrix, NSk(G ) is the orthogonalcomplement of CSk(G ).

A graph is always winnable mod k if and only ifdimNSk(G ) = 0.

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L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Remember that N~y 2 CSk(G ).

N~y = �~x is solvable if ~x is winnable.

Thus, ~x is winnable if and only if ~x 2 CSk(G ).

(Null Space of G - NSk(G ))

Since N is a symmetric matrix, NSk(G ) is the orthogonalcomplement of CSk(G ).

A graph is always winnable mod k if and only ifdimNSk(G ) = 0.

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Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

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Our Research Focus

~x is winnable if and only if ~x 2 CSk(G ).

A graph is always winnable mod k if and only ifdimNSk(G ) = 0.

NSk(G ) is the orthogonal complement of CSk(G ).

Characterize the way the null space changes when certainsubgraphs are removed, or when two graphs are joinedtogether.

Look for ways to connect graphs or remove subgraphs thatdo not change the null space.

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L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Our Research Focus

~x is winnable if and only if ~x 2 CSk(G ).

A graph is always winnable mod k if and only ifdimNSk(G ) = 0.

NSk(G ) is the orthogonal complement of CSk(G ).

Characterize the way the null space changes when certainsubgraphs are removed, or when two graphs are joinedtogether.

Look for ways to connect graphs or remove subgraphs thatdo not change the null space.

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Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Our Research Focus

~x is winnable if and only if ~x 2 CSk(G ).

A graph is always winnable mod k if and only ifdimNSk(G ) = 0.

NSk(G ) is the orthogonal complement of CSk(G ).

Characterize the way the null space changes when certainsubgraphs are removed, or when two graphs are joinedtogether.

Look for ways to connect graphs or remove subgraphs thatdo not change the null space.

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 28 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Our Research Focus

~x is winnable if and only if ~x 2 CSk(G ).

A graph is always winnable mod k if and only ifdimNSk(G ) = 0.

NSk(G ) is the orthogonal complement of CSk(G ).

Characterize the way the null space changes when certainsubgraphs are removed, or when two graphs are joinedtogether.

Look for ways to connect graphs or remove subgraphs thatdo not change the null space.

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Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

Our Research Focus

~x is winnable if and only if ~x 2 CSk(G ).

A graph is always winnable mod k if and only ifdimNSk(G ) = 0.

NSk(G ) is the orthogonal complement of CSk(G ).

Characterize the way the null space changes when certainsubgraphs are removed, or when two graphs are joinedtogether.

Look for ways to connect graphs or remove subgraphs thatdo not change the null space.

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L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

The Null Space

By definition, if ~z 2 NSk(G ), N~z = ~0

Then ~z is a null pattern that will not change the state ofgraph G , since N~z + ~x = ~x .

B

C

A

D

~z =

0

BB@

1100

1

CCA

ABCD

In Z2

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Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

The Null Space

By definition, if ~z 2 NSk(G ), N~z = ~0

Then ~z is a null pattern that will not change the state ofgraph G , since N~z + ~x = ~x .

B

C

A

D

~z =

0

BB@

1100

1

CCA

ABCD

In Z2

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 29 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

The Null Space

By definition, if ~z 2 NSk(G ), N~z = ~0

Then ~z is a null pattern that will not change the state ofgraph G , since N~z + ~x = ~x .

B

C

A

D

~z =

0

BB@

1100

1

CCA

ABCD

In Z2

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 29 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

The Null Space

By definition, if ~z 2 NSk(G ), N~z = ~0

Then ~z is a null pattern that will not change the state ofgraph G , since N~z + ~x = ~x .

B

C

A

D

~z =

0

BB@

1100

1

CCA

ABCD

In Z2

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 29 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

The Null Space

By definition, if ~z 2 NSk(G ), N~z = ~0

Then ~z is a null pattern that will not change the state ofgraph G , since N~z + ~x = ~x .

B

C

A

D

~z =

0

BB@

1100

1

CCA

ABCD

In Z2

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 29 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

The Null Space

By definition, if ~z 2 NSk(G ), N~z = ~0

Then ~z is a null pattern that will not change the state ofgraph G , since N~z + ~x = ~x .

B

C

A

D

~z =

0

BB@

1100

1

CCA

ABCD

In Z2

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 30 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

The Null Space

By definition, if ~z 2 NSk(G ), N~z = ~0

Then ~z is a null pattern that will not change the state ofgraph G , since N~z + ~x = ~x .

1

1

1

B

C

A

D

~z =

0

BB@

1100

1

CCA

ABCD

In Z2

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 31 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

The Null Space

By definition, if ~z 2 NSk(G ), N~z = ~0

Then ~z is a null pattern that will not change the state ofgraph G , since N~z + ~x = ~x .

1

1

1

B

C

A

D

~z =

0

BB@

1100

1

CCA

ABCD

In Z2

L. Ballard (Syracuse University) Lights Out on Related Graphs October 16, 2015 32 / 53

Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

The Null Space

By definition, if ~z 2 NSk(G ), N~z = ~0

Then ~z is a null pattern that will not change the state ofgraph G , since N~z + ~x = ~x .

B

C

A

D

~z =

0

BB@

1100

1

CCA

ABCD

In Z2

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L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

The Null Space

This null pattern can be generalized to Zk .

B

C

A

D

~z =

0

BB@

t�t00

1

CCA

ABCD

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L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

The Null Space

This null pattern can be generalized to Zk .

B

C

A

D

~z =

0

BB@

t�t00

1

CCA

ABCD

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Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

The Null Space

This null pattern can be generalized to Zk .

t

t

t

B

C

A

D

~z =

0

BB@

t�t00

1

CCA

ABCD

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Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

The Null Space

This null pattern can be generalized to Zk .

t

t

t

B

C

A

D

~z =

0

BB@

t�t00

1

CCA

ABCD

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Lights Out onRelatedGraphs

L. Ballard

Lights OutIntroductionLinear Algebra

ResearchNull SpaceTheorems

ConclusionAcknowledg-mentsReferences

The Null Space

This null pattern can be generalized to Zk .

B

C

A

D

~z =

0

BB@

t�t00

1

CCA

ABCD

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A Sampling of Our Results

Definition

The label of a vertex v in a graph G will be defined by

lG (v) = dimNSk(G � v)� dimNSk(G ).

In other words, dimNSk(G � v) = dimNSk(G ) + lG (v)

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A Sampling of Our Results

Proposition

Let G be a graph. For all v 2 V (G ), we havelG (v) 2 {�1, 0, 1}. If G is always winnable over Zk , then forall v 2 V (G ), we have lG (v) 2 {0, 1}.

Proof. The neighborhood matrix of G � v is formed by deletingexactly one row and one column from the neighborhood matrixof G . Thus lG (v) 2 {�1, 0, 1}. For an always winnable graphG , dimNSk(G ) = 0, and therefore for all v 2 V (G ), we havedimNSk(G � v) � dimNSk(G ), so lG (v) 2 {0, 1}.

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A Sampling of Our Results

Proposition

Let G be a graph. For all v 2 V (G ), we havelG (v) 2 {�1, 0, 1}. If G is always winnable over Zk , then forall v 2 V (G ), we have lG (v) 2 {0, 1}.

Proof. The neighborhood matrix of G � v is formed by deletingexactly one row and one column from the neighborhood matrixof G .

Thus lG (v) 2 {�1, 0, 1}. For an always winnable graphG , dimNSk(G ) = 0, and therefore for all v 2 V (G ), we havedimNSk(G � v) � dimNSk(G ), so lG (v) 2 {0, 1}.

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A Sampling of Our Results

Proposition

Let G be a graph. For all v 2 V (G ), we havelG (v) 2 {�1, 0, 1}. If G is always winnable over Zk , then forall v 2 V (G ), we have lG (v) 2 {0, 1}.

Proof. The neighborhood matrix of G � v is formed by deletingexactly one row and one column from the neighborhood matrixof G . Thus lG (v) 2 {�1, 0, 1}.

For an always winnable graphG , dimNSk(G ) = 0, and therefore for all v 2 V (G ), we havedimNSk(G � v) � dimNSk(G ), so lG (v) 2 {0, 1}.

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A Sampling of Our Results

Proposition

Let G be a graph. For all v 2 V (G ), we havelG (v) 2 {�1, 0, 1}. If G is always winnable over Zk , then forall v 2 V (G ), we have lG (v) 2 {0, 1}.

Proof. The neighborhood matrix of G � v is formed by deletingexactly one row and one column from the neighborhood matrixof G . Thus lG (v) 2 {�1, 0, 1}. For an always winnable graphG , dimNSk(G ) = 0, and therefore for all v 2 V (G ), we havedimNSk(G � v) � dimNSk(G ), so lG (v) 2 {0, 1}.

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A Sampling of Our Results

Proposition

If there exists ~p 2 NSk(G ) with ~p(v) 6= 0, then lG (v) = �1.

Suppose ~p 2 NSk(G ) such that ~p(v) 6= 0. Then ev is notwinnable on G , since ev is not in the orthogonal complementof NSk(G ). It follows that a pattern on G that is null on G � vis also null at v ; otherwise that pattern would win �ev for some� 2 Z⇤

k . In particular, a null pattern on G � v extended by 0 atv is null on G , so dimNSk(G ) � dimNSk(G � v)

.

The factthat there exists a null pattern ~p 2 NSk(G ) not of this typegives us a strict inequality, or in other words gives uslG (v) = �1.

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A Sampling of Our Results

Proposition

If there exists ~p 2 NSk(G ) with ~p(v) 6= 0, then lG (v) = �1.

Suppose ~p 2 NSk(G ) such that ~p(v) 6= 0.

Then ev is notwinnable on G , since ev is not in the orthogonal complementof NSk(G ). It follows that a pattern on G that is null on G � vis also null at v ; otherwise that pattern would win �ev for some� 2 Z⇤

k . In particular, a null pattern on G � v extended by 0 atv is null on G , so dimNSk(G ) � dimNSk(G � v)

.

The factthat there exists a null pattern ~p 2 NSk(G ) not of this typegives us a strict inequality, or in other words gives uslG (v) = �1.

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A Sampling of Our Results

Proposition

If there exists ~p 2 NSk(G ) with ~p(v) 6= 0, then lG (v) = �1.

Suppose ~p 2 NSk(G ) such that ~p(v) 6= 0. Then ev is notwinnable on G , since ev is not in the orthogonal complementof NSk(G ).

It follows that a pattern on G that is null on G � vis also null at v ; otherwise that pattern would win �ev for some� 2 Z⇤

k . In particular, a null pattern on G � v extended by 0 atv is null on G , so dimNSk(G ) � dimNSk(G � v)

.

The factthat there exists a null pattern ~p 2 NSk(G ) not of this typegives us a strict inequality, or in other words gives uslG (v) = �1.

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A Sampling of Our Results

Proposition

If there exists ~p 2 NSk(G ) with ~p(v) 6= 0, then lG (v) = �1.

Suppose ~p 2 NSk(G ) such that ~p(v) 6= 0. Then ev is notwinnable on G , since ev is not in the orthogonal complementof NSk(G ). It follows that a pattern on G that is null on G � vis also null at v ; otherwise that pattern would win �ev for some� 2 Z⇤

k .

In particular, a null pattern on G � v extended by 0 atv is null on G , so dimNSk(G ) � dimNSk(G � v)

.

The factthat there exists a null pattern ~p 2 NSk(G ) not of this typegives us a strict inequality, or in other words gives uslG (v) = �1.

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A Sampling of Our Results

Proposition

If there exists ~p 2 NSk(G ) with ~p(v) 6= 0, then lG (v) = �1.

Suppose ~p 2 NSk(G ) such that ~p(v) 6= 0. Then ev is notwinnable on G , since ev is not in the orthogonal complementof NSk(G ). It follows that a pattern on G that is null on G � vis also null at v ; otherwise that pattern would win �ev for some� 2 Z⇤

k . In particular, a null pattern on G � v extended by 0 atv is null on G , so dimNSk(G ) � dimNSk(G � v).

The factthat there exists a null pattern ~p 2 NSk(G ) not of this typegives us a strict inequality, or in other words gives uslG (v) = �1.

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A Sampling of Our Results

Proposition

If there exists ~p 2 NSk(G ) with ~p(v) 6= 0, then lG (v) = �1.

Suppose ~p 2 NSk(G ) such that ~p(v) 6= 0. Then ev is notwinnable on G , since ev is not in the orthogonal complementof NSk(G ). It follows that a pattern on G that is null on G � vis also null at v ; otherwise that pattern would win �ev for some� 2 Z⇤

k . In particular, a null pattern on G � v extended by 0 atv is null on G , so dimNSk(G ) � dimNSk(G � v). The factthat there exists a null pattern ~p 2 NSk(G ) not of this typegives us a strict inequality, or in other words gives uslG (v) = �1.

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Corollary

Let G be a graph, and let v 2 V (G ). Then if lG (v) = 0,~p(v) = 0 for every ~p 2 NSk(G ).

Proof. If lG (v) = 0, then lG (v) 6= �1, so by the contrapositiveof the previous proposition, ~p(v) = 0 for every ~p 2 NSk(G ).

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Corollary

Let G be a graph, and let v 2 V (G ). Then if lG (v) = 0,~p(v) = 0 for every ~p 2 NSk(G ).

Proof. If lG (v) = 0, then lG (v) 6= �1, so by the contrapositiveof the previous proposition, ~p(v) = 0 for every ~p 2 NSk(G ).

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A Sampling of Our Results

Proposition

Let G be a graph and let v 2 V (G ). If lG (v) = 0, then for all� 2 Z⇤

k , the state �ev is winnable on G , and any winningpattern ~p for �ev satisfies p(v) 6= 0.

Proof. Suppose that lG (v) = 0. Then by the previouscorollary, ~q(v) = 0 for every ~q 2 NSk(G ). The space ofwinnable states is the orthogonal complement of the space ofnull patterns, and therefore, for all � 2 Z⇤

k , �ev is winnablebecause �ev ? ~q for all ~q 2 NSk(G ).

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A Sampling of Our Results

Proposition

Let G be a graph and let v 2 V (G ). If lG (v) = 0, then for all� 2 Z⇤

k , the state �ev is winnable on G , and any winningpattern ~p for �ev satisfies p(v) 6= 0.

Proof. Suppose that lG (v) = 0.

Then by the previouscorollary, ~q(v) = 0 for every ~q 2 NSk(G ). The space ofwinnable states is the orthogonal complement of the space ofnull patterns, and therefore, for all � 2 Z⇤

k , �ev is winnablebecause �ev ? ~q for all ~q 2 NSk(G ).

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Proposition

Let G be a graph and let v 2 V (G ). If lG (v) = 0, then for all� 2 Z⇤

k , the state �ev is winnable on G , and any winningpattern ~p for �ev satisfies p(v) 6= 0.

Proof. Suppose that lG (v) = 0. Then by the previouscorollary, ~q(v) = 0 for every ~q 2 NSk(G ).

The space ofwinnable states is the orthogonal complement of the space ofnull patterns, and therefore, for all � 2 Z⇤

k , �ev is winnablebecause �ev ? ~q for all ~q 2 NSk(G ).

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Proposition

Let G be a graph and let v 2 V (G ). If lG (v) = 0, then for all� 2 Z⇤

k , the state �ev is winnable on G , and any winningpattern ~p for �ev satisfies p(v) 6= 0.

Proof. Suppose that lG (v) = 0. Then by the previouscorollary, ~q(v) = 0 for every ~q 2 NSk(G ). The space ofwinnable states is the orthogonal complement of the space ofnull patterns, and therefore, for all � 2 Z⇤

k , �ev is winnablebecause �ev ? ~q for all ~q 2 NSk(G ).

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Proposition

Let G be a graph and let v 2 V (G ). Then if lG (v) = 0, thenfor all � 2 Z⇤

k , the state �ev is winnable on G , and any winningpattern ~p for �ev satisfies p(v) 6= 0.

Assume for the sake of contradiction that ~p is a winningpattern for �ev such that ~p(v) = 0. It follows that ~p|G�v isnull, but ~p is not null on G . We also know that for all~q 2 NSk(G ), ~q(v) = 0 and thus ~q|G�v is always a null patternon G � v . We note that ~p|G�v must be distinct from ~q|G�v forall ~q 2 NSk(G ), since the e↵ect of extending these patterns by0 at v is di↵erent. This implies thatdimNSk(G � v) > dimNSk(G ), contradicting the fact thatlG (v) = 0. Thus ~p(v) 6= 0.

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Proposition

Let G be a graph and let v 2 V (G ). Then if lG (v) = 0, thenfor all � 2 Z⇤

k , the state �ev is winnable on G , and any winningpattern ~p for �ev satisfies p(v) 6= 0.

Assume for the sake of contradiction that ~p is a winningpattern for �ev such that ~p(v) = 0.

It follows that ~p|G�v isnull, but ~p is not null on G . We also know that for all~q 2 NSk(G ), ~q(v) = 0 and thus ~q|G�v is always a null patternon G � v . We note that ~p|G�v must be distinct from ~q|G�v forall ~q 2 NSk(G ), since the e↵ect of extending these patterns by0 at v is di↵erent. This implies thatdimNSk(G � v) > dimNSk(G ), contradicting the fact thatlG (v) = 0. Thus ~p(v) 6= 0.

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Proposition

Let G be a graph and let v 2 V (G ). Then if lG (v) = 0, thenfor all � 2 Z⇤

k , the state �ev is winnable on G , and any winningpattern ~p for �ev satisfies p(v) 6= 0.

Assume for the sake of contradiction that ~p is a winningpattern for �ev such that ~p(v) = 0. It follows that ~p|G�v isnull, but ~p is not null on G .

We also know that for all~q 2 NSk(G ), ~q(v) = 0 and thus ~q|G�v is always a null patternon G � v . We note that ~p|G�v must be distinct from ~q|G�v forall ~q 2 NSk(G ), since the e↵ect of extending these patterns by0 at v is di↵erent. This implies thatdimNSk(G � v) > dimNSk(G ), contradicting the fact thatlG (v) = 0. Thus ~p(v) 6= 0.

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Proposition

Let G be a graph and let v 2 V (G ). Then if lG (v) = 0, thenfor all � 2 Z⇤

k , the state �ev is winnable on G , and any winningpattern ~p for �ev satisfies p(v) 6= 0.

Assume for the sake of contradiction that ~p is a winningpattern for �ev such that ~p(v) = 0. It follows that ~p|G�v isnull, but ~p is not null on G . We also know that for all~q 2 NSk(G ), ~q(v) = 0 and thus ~q|G�v is always a null patternon G � v .

We note that ~p|G�v must be distinct from ~q|G�v forall ~q 2 NSk(G ), since the e↵ect of extending these patterns by0 at v is di↵erent. This implies thatdimNSk(G � v) > dimNSk(G ), contradicting the fact thatlG (v) = 0. Thus ~p(v) 6= 0.

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Proposition

Let G be a graph and let v 2 V (G ). Then if lG (v) = 0, thenfor all � 2 Z⇤

k , the state �ev is winnable on G , and any winningpattern ~p for �ev satisfies p(v) 6= 0.

Assume for the sake of contradiction that ~p is a winningpattern for �ev such that ~p(v) = 0. It follows that ~p|G�v isnull, but ~p is not null on G . We also know that for all~q 2 NSk(G ), ~q(v) = 0 and thus ~q|G�v is always a null patternon G � v . We note that ~p|G�v must be distinct from ~q|G�v forall ~q 2 NSk(G ), since the e↵ect of extending these patterns by0 at v is di↵erent.

This implies thatdimNSk(G � v) > dimNSk(G ), contradicting the fact thatlG (v) = 0. Thus ~p(v) 6= 0.

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Proposition

Let G be a graph and let v 2 V (G ). Then if lG (v) = 0, thenfor all � 2 Z⇤

k , the state �ev is winnable on G , and any winningpattern ~p for �ev satisfies p(v) 6= 0.

Assume for the sake of contradiction that ~p is a winningpattern for �ev such that ~p(v) = 0. It follows that ~p|G�v isnull, but ~p is not null on G . We also know that for all~q 2 NSk(G ), ~q(v) = 0 and thus ~q|G�v is always a null patternon G � v . We note that ~p|G�v must be distinct from ~q|G�v forall ~q 2 NSk(G ), since the e↵ect of extending these patterns by0 at v is di↵erent. This implies thatdimNSk(G � v) > dimNSk(G ), contradicting the fact thatlG (v) = 0.

Thus ~p(v) 6= 0.

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Proposition

Let G be a graph and let v 2 V (G ). Then if lG (v) = 0, thenfor all � 2 Z⇤

k , the state �ev is winnable on G , and any winningpattern ~p for �ev satisfies p(v) 6= 0.

Assume for the sake of contradiction that ~p is a winningpattern for �ev such that ~p(v) = 0. It follows that ~p|G�v isnull, but ~p is not null on G . We also know that for all~q 2 NSk(G ), ~q(v) = 0 and thus ~q|G�v is always a null patternon G � v . We note that ~p|G�v must be distinct from ~q|G�v forall ~q 2 NSk(G ), since the e↵ect of extending these patterns by0 at v is di↵erent. This implies thatdimNSk(G � v) > dimNSk(G ), contradicting the fact thatlG (v) = 0. Thus ~p(v) 6= 0.

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Definition (The Secondary Label of v in G )

1. Let G be a graph and suppose v 2 V (G ) with lG (v) = 0.By the previous proposition, the state ev has a winningpattern ~q, and ~q(v) 2 Z⇤

k . Let

�G (v) = �~q(v)�1 2 Z⇤k .

In this situation, all null patterns ~p on G have ~p(v) = 0,and therefore �G (v) is independent of the winning pattern~q chosen.

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Definition (The Secondary Label of v in G )

1. Let G be a graph and suppose v 2 V (G ) with lG (v) = 0.By the previous proposition, the state ev has a winningpattern ~q, and ~q(v) 2 Z⇤

k . Let

�G (v) = �~q(v)�1 2 Z⇤k .

In this situation, all null patterns ~p on G have ~p(v) = 0,and therefore �G (v) is independent of the winning pattern~q chosen.

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Definition

2. Let G be a graph and suppose v 2 V (G ) withlG (v) = �1. We define �G (v) = 0. (This secondary labelon the lG (v) = �1 vertices carries no information, but isconvenient for summation notation later.)

In either case, �G (v) 2 Z⇤k will be called the secondary label

of v . The label of a vertex v with lG (v) = 0 and secondarylabel � will typically be written as 0(�).

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Definition

2. Let G be a graph and suppose v 2 V (G ) withlG (v) = �1. We define �G (v) = 0. (This secondary labelon the lG (v) = �1 vertices carries no information, but isconvenient for summation notation later.)

In either case, �G (v) 2 Z⇤k will be called the secondary label

of v . The label of a vertex v with lG (v) = 0 and secondarylabel � will typically be written as 0(�).

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Definition (Edge Join of G1 and G2 at v and w , respectively)

Let G1 and G2 be graphs with v 2 V (G1) and w 2 V (G2). LetH = EJ({G1, v}{G2,w}) be the graph withV (H) = V (G1) [ V (G2) and E (H) = E (G1) [ E (G2) [ (v ,w).

G2G1

v w

H

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Definition (Edge Join of G1 and G2 at v and w , respectively)

Let G1 and G2 be graphs with v 2 V (G1) and w 2 V (G2). LetH = EJ({G1, v}{G2,w}) be the graph withV (H) = V (G1) [ V (G2) and E (H) = E (G1) [ E (G2) [ (v ,w).

G2G1

v w

H

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Definition (Edge Join of G1 and G2 at v and w , respectively)

Let G1 and G2 be graphs with v 2 V (G1) and w 2 V (G2). LetH = EJ({G1, v}{G2,w}) be the graph withV (H) = V (G1) [ V (G2) and E (H) = E (G1) [ E (G2) [ (v ,w).

G2G1

v w

H

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Theorem

Let G1 and G2 be graphs with v 2 V (G1) and w 2 V (G2). Letdi = dimNSk(Gi ), and let H = EJ({G1, v}{G2,w}). ThendimNSk(H) is given by the following table.

lG1(v) lG2(w) dimNSk(H)

1 any d1 + d2�1 any d1 + d2 + lG2(w)� 10(�) 0(µ) d1 + d2 (µ 6= ��1)0(�) 0(µ) d1 + d2 + 1 (µ = ��1)

In particular, if lG1(v) = �1, thendimNSk(H) = dimNSk(G1 � v) + dimNSk(G2 � w).

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Vertex joining:

G1 G2

H

v1 v2

v

The following theorem will show how NSk(H) depends onlGi

(vi ) for i 2 {1, 2}.

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Vertex joining:

G1 G2

H

v1 v2

v

The following theorem will show how NSk(H) depends onlGi

(vi ) for i 2 {1, 2}.

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Vertex joining:

G1 G2

H

v1 v2

v

The following theorem will show how NSk(H) depends onlGi

(vi ) for i 2 {1, 2}.

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Vertex joining:

G1 G2

H

v1 v2

v

The following theorem will show how NSk(H) depends onlGi

(vi ) for i 2 {1, 2}.

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Theorem

For 1 i m, let Gi be a finite graph with vi 2 V (Gi ). Thegraph H = VJ({Gi , vi : 1 i m}) is defined by

V (H) =m[

i=1

V (Gi � vi ) [ {v} and

E (H) =m[

i=1

E (Gi � vi ) [((wv) : (wvi ) 2

m[

i=1

E (Gi )

).

1 If lGi(vi ) = 1 for at least one i , then lH(v) = 1.

2 lH(v) 2 {0,�1} if and only if lGi(vi ) 2 {0,�1} for all i .

Moreover, lH(v) = �1 if and only ifmX

i=1

�Gi(vi ) = m � 1( mod k).

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Theorem

For 1 i m, let Gi be a finite graph with vi 2 V (Gi ). Thegraph H = VJ({Gi , vi : 1 i m}) is defined by

V (H) =m[

i=1

V (Gi � vi ) [ {v} and

E (H) =m[

i=1

E (Gi � vi ) [((wv) : (wvi ) 2

m[

i=1

E (Gi )

).

1 If lGi(vi ) = 1 for at least one i , then lH(v) = 1.

2 lH(v) 2 {0,�1} if and only if lGi(vi ) 2 {0,�1} for all i .

Moreover, lH(v) = �1 if and only ifmX

i=1

�Gi(vi ) = m � 1( mod k).

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Theorem

For 1 i m, let Gi be a finite graph with vi 2 V (Gi ). Thegraph H = VJ({Gi , vi : 1 i m}) is defined by

V (H) =m[

i=1

V (Gi � vi ) [ {v} and

E (H) =m[

i=1

E (Gi � vi ) [((wv) : (wvi ) 2

m[

i=1

E (Gi )

).

1 If lGi(vi ) = 1 for at least one i , then lH(v) = 1.

2 lH(v) 2 {0,�1} if and only if lGi(vi ) 2 {0,�1} for all i .

Moreover, lH(v) = �1 if and only ifmX

i=1

�Gi(vi ) = m � 1( mod k).

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Acknowledgments

I would like to acknowledge:

Syracuse University MGO

Dr. Darin Stephenson

Hope College

The National Science Foundation

Drs. Kristin Camenga and Rebekah Yates

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References

Anderson, M., & Feil, T. (1998). Turning lights out with linearalgebra. Mathematics Magazine, 71(4), 300-303.

Edwards, S., Elandt, V., James, N., Johnson, K., Mitchell, Z.,& Stephenson, D. (2008). Lights out on finite graphs. 1-13.

Gi↵en, A., & Parker, D. (2009). On generalizing the“lightsout” game and a generalization of parity domination. 1-14.

Stephenson, D. R. (2012). Lights out, �+-automata, anddomination in graphs. 1-10.

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Theorem

Let G be a finite graph with v 2 V (G ), and let fv be the

function which extends a pattern on G � v to a pattern on

G that is zero at v . The following are equivalent:

1 lG (v) = �1,

2The state ev is not winnable on G .

3There exists p 2 Null(N(G )) with p(v) 6= 0.

4The function fv induces an injective linear

transformation from Null(N(G � v)) to Null(N(G )), anddim coker(fv ) = 1.

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Theorem

Let G be a finite graph with v 2 V (G ), and let fv be the

function which extends a pattern on G � v to a pattern on

G that is zero at v . The following are equivalent:

1 lG (v) = �1,

2The state ev is not winnable on G .

3There exists p 2 Null(N(G )) with p(v) 6= 0.

4The function fv induces an injective linear

transformation from Null(N(G � v)) to Null(N(G )), anddim coker(fv ) = 1.

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Theorem

Let G be a finite graph with v 2 V (G ), and let fv be the

function which extends a pattern on G � v to a pattern on

G that is zero at v . The following are equivalent:

1 lG (v) = �1,

2The state ev is not winnable on G .

3There exists p 2 Null(N(G )) with p(v) 6= 0.

4The function fv induces an injective linear

transformation from Null(N(G � v)) to Null(N(G )), anddim coker(fv ) = 1.

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Theorem

Let G be a finite graph with v 2 V (G ), and let fv be the

function which extends a pattern on G � v to a pattern on

G that is zero at v . The following are equivalent:

1 lG (v) = �1,

2The state ev is not winnable on G .

3There exists p 2 Null(N(G )) with p(v) 6= 0.

4The function fv induces an injective linear

transformation from Null(N(G � v)) to Null(N(G )), anddim coker(fv ) = 1.

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Theorem

Let G be a finite graph with v 2 V (G ), and let fv be the

function which extends a pattern on G � v to a pattern on

G that is zero at v . The following are equivalent:

1 lG (v) = �1,

2The state ev is not winnable on G .

3There exists p 2 Null(N(G )) with p(v) 6= 0.

4The function fv induces an injective linear

transformation from Null(N(G � v)) to Null(N(G )), anddim coker(fv ) = 1.

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