Two graphs $G$ and $H$ are isomorphic if they have a function $f$ which provides an exact pairing of vertices in the two graphs such that for any adjacent vertices $u,v\in \{\mbox{set of vertices of }G\}$, $f(u)$ and $f(v)$ are also adjacent in $H$.

learn more… | top users | synonyms

2
votes
2answers
54 views

Number of Labels used in reduction of Isomorphism of Labelled Graph to Graph Isomorphism

From "Lecture Notes in Computer Science" by Christoph M. Hoffmann , Assume that both $X$ and $X'$ have $n$ vertices. We plan to code the graph labels as suitable subgraphs which we attach to the ...
22
votes
4answers
8k views

Are these 2 graphs isomorphic?

They meet the requirements of both having an $=$ number of vertices ($7$). They both have the same number of edges ($9$). They both have $3$ vertices of degree $2$ and $4$ of degree $3$. However, ...
8
votes
2answers
390 views

Reorder adjacency matrices of regular graphs so they are the same

Given a matrix A of a strongly $k$ regular graph G(srg($n,k,\lambda,\mu$);$\lambda ,\mu >0;k>3$). The matrix A can be divided into 4 sub matrices based on adjacency of vertex $x \in G$. $A_x$ ...
2
votes
2answers
84 views

Automorphism group of a graph = Automorphism group of that graph's adjacency matrix?

Is automorphism group (or set) of a graph $G$ equal to the automorphism group (or set) of adjacency matrix of $G$? Example: $G_1, G_2$ are separate graphs where $G_1^{\pi}= G_2$ and $ G= \bar ...
4
votes
1answer
39 views

How to detect automorphism of union of graphs?

On page 1 of Lecture 2, Algebra and Computation , (Course Instructor: V. Arvind), there is a theorem- Theorem 2. With Graph − Iso (graph isomorphism) as an oracle, there is a polynomial time ...
3
votes
1answer
52 views

Confusion about the hidden subgroup formulation of graph isomorphism

I am going through Quantum factoring, discrete logarithms and the hidden subgroup problem by Richard Jozsa. On page 13, the author discussed the hidden subgroup problem (HSP) formulation of the graph ...
3
votes
2answers
93 views

Is $\exp:\mathbb{M_n}\to\mathbb{M_n}$ injective?

This is related to a personal exploration of isometries of directed graphs, motivated by my son's Lego Duplo train tracks and identifying "interesting" layouts. If $M$ is the adjacency matrix for a ...
3
votes
2answers
6k views

How to find non-isomorphic trees?

"Draw all non-isomorphic trees with 5 vertices." I have searched the web and found many examples of the non-isomorphic trees with 5 vertices, but I can't figure out how they have come to their ...
4
votes
3answers
159 views

How Graph Isomorphism is used to determine Graph Automorphism?

From Lecture 2, Algebra and Computation by V. Arvind, (page2,3), I understood below passage- For our graph $G$, let $Aut(G) = H ≤ S_n$. We shall use Weilandt’s notation where $i^\pi$ denotes ...
4
votes
1answer
29 views

What is the meaning of saying “two graph vertices are in correspondence?”

What are the conditions for two graphs to be in correspondence? I know for isomorphic - Two graphs which contain the same number of graph vertices connected in the same way are said to be isomorphic. ...
2
votes
1answer
396 views

Proving that a graph is self complementary

I've been given the following adjacency matrix: $$\left(\begin{array}{cccccccc} 0 & 1 & 0 & 0 & 1 & 0 & 0 & 1 \\ 1 & 0 & 1 & 1 & 0 & 0 & 0 & 1 ...
1
vote
1answer
445 views

Number of isomorphism classes of a tree on n vertices

I'm currently trying to solve this problem: "Show that the number of isomorphism classes of tree on n vertices is at least $\frac{n^{n-2}}{n!}$." I'm pretty stumped to be honest. I know of Cayley's ...
0
votes
1answer
66 views

How can I show complete graphs are determined by spectrum?

I understand how to prove a complete graph $K_n$ has spectrum $\lbrace -1^{(n-1)},n-1 \rbrace$. However I am having difficulty proving that the spectrum uniquely determines the complete graph. ...