A notion of adjacency-matrix symmetry?












3












$begingroup$


I have a set of adjacency matrices that have a certain property, and I am trying to figure out what features of the adjacency matrix deliver that property and whether this property has a name.



Here is the property: Let $A$ be an adjacency matrix for an undirected graph. Such a matrix has Property $X$ if all the diagonal elements of $A$ are the same (which of course they are trivially), all the diagonal elements of $A^2$ are the same, all the diagonal elements of $A^3$ are the same, and so on for all powers of $A$.



Another way of describing this property is that for each node $i$, there are the same number of walks of length $k$ from node $i$ to itself for all $k$.



Thanks!










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  • $begingroup$
    "... for all $i$'', not "for all $k$", I suppose?
    $endgroup$
    – W-t-P
    Jan 19 at 7:47
















3












$begingroup$


I have a set of adjacency matrices that have a certain property, and I am trying to figure out what features of the adjacency matrix deliver that property and whether this property has a name.



Here is the property: Let $A$ be an adjacency matrix for an undirected graph. Such a matrix has Property $X$ if all the diagonal elements of $A$ are the same (which of course they are trivially), all the diagonal elements of $A^2$ are the same, all the diagonal elements of $A^3$ are the same, and so on for all powers of $A$.



Another way of describing this property is that for each node $i$, there are the same number of walks of length $k$ from node $i$ to itself for all $k$.



Thanks!










share|cite|improve this question











$endgroup$












  • $begingroup$
    "... for all $i$'', not "for all $k$", I suppose?
    $endgroup$
    – W-t-P
    Jan 19 at 7:47














3












3








3





$begingroup$


I have a set of adjacency matrices that have a certain property, and I am trying to figure out what features of the adjacency matrix deliver that property and whether this property has a name.



Here is the property: Let $A$ be an adjacency matrix for an undirected graph. Such a matrix has Property $X$ if all the diagonal elements of $A$ are the same (which of course they are trivially), all the diagonal elements of $A^2$ are the same, all the diagonal elements of $A^3$ are the same, and so on for all powers of $A$.



Another way of describing this property is that for each node $i$, there are the same number of walks of length $k$ from node $i$ to itself for all $k$.



Thanks!










share|cite|improve this question











$endgroup$




I have a set of adjacency matrices that have a certain property, and I am trying to figure out what features of the adjacency matrix deliver that property and whether this property has a name.



Here is the property: Let $A$ be an adjacency matrix for an undirected graph. Such a matrix has Property $X$ if all the diagonal elements of $A$ are the same (which of course they are trivially), all the diagonal elements of $A^2$ are the same, all the diagonal elements of $A^3$ are the same, and so on for all powers of $A$.



Another way of describing this property is that for each node $i$, there are the same number of walks of length $k$ from node $i$ to itself for all $k$.



Thanks!







linear-algebra matrices graph-theory






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edited Jan 18 at 23:56







Mike

















asked Jan 18 at 23:10









MikeMike

368110




368110












  • $begingroup$
    "... for all $i$'', not "for all $k$", I suppose?
    $endgroup$
    – W-t-P
    Jan 19 at 7:47


















  • $begingroup$
    "... for all $i$'', not "for all $k$", I suppose?
    $endgroup$
    – W-t-P
    Jan 19 at 7:47
















$begingroup$
"... for all $i$'', not "for all $k$", I suppose?
$endgroup$
– W-t-P
Jan 19 at 7:47




$begingroup$
"... for all $i$'', not "for all $k$", I suppose?
$endgroup$
– W-t-P
Jan 19 at 7:47










1 Answer
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The usual name for this property is walk regular. and google will quickly lead to a lot of information. Clearly any vertex-transitive graph is walk regular, more generally any graph that is a union of classes from an association scheme. Connected regular graphs with exactly four eigenvalues are another class. I do not know of a characterization of walk-regular graphs that is much better than the definition.






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    $begingroup$

    The usual name for this property is walk regular. and google will quickly lead to a lot of information. Clearly any vertex-transitive graph is walk regular, more generally any graph that is a union of classes from an association scheme. Connected regular graphs with exactly four eigenvalues are another class. I do not know of a characterization of walk-regular graphs that is much better than the definition.






    share|cite|improve this answer









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      4












      $begingroup$

      The usual name for this property is walk regular. and google will quickly lead to a lot of information. Clearly any vertex-transitive graph is walk regular, more generally any graph that is a union of classes from an association scheme. Connected regular graphs with exactly four eigenvalues are another class. I do not know of a characterization of walk-regular graphs that is much better than the definition.






      share|cite|improve this answer









      $endgroup$
















        4












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        4





        $begingroup$

        The usual name for this property is walk regular. and google will quickly lead to a lot of information. Clearly any vertex-transitive graph is walk regular, more generally any graph that is a union of classes from an association scheme. Connected regular graphs with exactly four eigenvalues are another class. I do not know of a characterization of walk-regular graphs that is much better than the definition.






        share|cite|improve this answer









        $endgroup$



        The usual name for this property is walk regular. and google will quickly lead to a lot of information. Clearly any vertex-transitive graph is walk regular, more generally any graph that is a union of classes from an association scheme. Connected regular graphs with exactly four eigenvalues are another class. I do not know of a characterization of walk-regular graphs that is much better than the definition.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Jan 19 at 16:30









        Chris GodsilChris Godsil

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