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Aaron Meyerowitz
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If $G$ and $H$ are isomorphic then a bijection between them does what you want (Though I could assure you that two graphs are isomorphic, be telling the truth, and yet it could be hard to find a bijection.) You seem to be interested in the situation that $G$ and $H$ are $n$ vertex graphs which are not isomorphic yet $(A_g)^k$ and ($A_H)^k$ have equal trace for all $1 \leq k \leq n.$

Do you have examples? Do you have examples that don't differ by an obvious switch? Even if you have a compact description of cycles, that doesn't give you a bijection short of ordering them somehow.

Here is a kind of silly example but tell me what bijection you would want:

Both graphs have two vertices and multiple parallel directed edges. The adjacency matrices are

$A_G=\begin{bmatrix} 0 & 1 \\ 4 & 0 \end{bmatrix}$ and $A_H=\begin{bmatrix} 0 & 2 \\ 2 & 0 \end{bmatrix}$

Even for very large $k>n$ the powers have the same trace , and are equal when the trace is not zero:

$A_G^k=A_H^k=\begin{bmatrix} 2^k &0 \\ 0 & 2^k \end{bmatrix}$ for $k$ even.

For odd $k$ we have $A_G^k=\begin{bmatrix} 0 & 1 \\ 4^k & 0 \end{bmatrix}$ and $A_H^k=\begin{bmatrix} 0 & 2^k \\ 2^k & 0 \end{bmatrix}$ both with trace $0.$

A picture is hardly needed but here is one with edge labels.

enter image description here

If you do not want multiple directed edges with the same head and tail then put a vertex at each letter.

LATER

Here is another silly example. The vertices named by letters have indegree=outdegree=$1$ whereas vertex k has indegree=outdegree=$k$

enter image description here

For $j=1,2,3,4,5$ the number of $j$ cycles is $0,9,0,25,0$ in both graphs. Not fully what you wanted, but what would your bijections be for $j=2$ and $j=4$?

We have $|G|=11$ with the $25$ $4$-cycles falling into $10$ of type $2d_i2d_j$ and $15$ of type $5e_i5e_j$

We have $|H|=12$ with the $25$ $4$-cycles falling into $1$ of type $1a1a,$ $3$ of type $4b_i4b_j$ and $21$ of type $6c_i6c_j$

Q: What is your bijection?

NOTES:

  • One could replace directed $2$-cycles by directed $3$-cycles without changing the example in an essential way.

  • I'm sure a way could be found to make a similar example such that the traces of $A_G^j$ and $A_H^j$ are equal for $1 \leq j \leq |G|.$

Aaron Meyerowitz
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