Identifier
Values
[2,2] => [[1,2],[3,4]] => [2,2] => ([(1,3),(2,3)],4) => 0
[3,2] => [[1,2,5],[3,4]] => [2,3] => ([(2,4),(3,4)],5) => 0
[2,2,1] => [[1,3],[2,5],[4]] => [3,2] => ([(1,4),(2,4),(3,4)],5) => 0
[4,2] => [[1,2,5,6],[3,4]] => [2,4] => ([(3,5),(4,5)],6) => 0
[3,3] => [[1,2,3],[4,5,6]] => [3,3] => ([(2,5),(3,5),(4,5)],6) => 0
[3,2,1] => [[1,3,6],[2,5],[4]] => [3,3] => ([(2,5),(3,5),(4,5)],6) => 0
[2,2,1,1] => [[1,4],[2,6],[3],[5]] => [4,2] => ([(1,5),(2,5),(3,5),(4,5)],6) => 0
[5,2] => [[1,2,5,6,7],[3,4]] => [2,5] => ([(4,6),(5,6)],7) => 0
[4,3] => [[1,2,3,7],[4,5,6]] => [3,4] => ([(3,6),(4,6),(5,6)],7) => 0
[4,2,1] => [[1,3,6,7],[2,5],[4]] => [3,4] => ([(3,6),(4,6),(5,6)],7) => 0
[3,3,1] => [[1,3,4],[2,6,7],[5]] => [4,3] => ([(2,6),(3,6),(4,6),(5,6)],7) => 0
[3,2,1,1] => [[1,4,7],[2,6],[3],[5]] => [4,3] => ([(2,6),(3,6),(4,6),(5,6)],7) => 0
[2,2,1,1,1] => [[1,5],[2,7],[3],[4],[6]] => [5,2] => ([(1,6),(2,6),(3,6),(4,6),(5,6)],7) => 0
search for individual values
searching the database for the individual values of this statistic
Description
The second largest eigenvalue of a graph if it is integral.
This statistic is undefined if the second largest eigenvalue of the graph is not integral.
Chapter 4 of [1] provides lots of context.
Map
to threshold graph
Description
The threshold graph corresponding to the composition.
A threshold graph is a graph that can be obtained from the empty graph by adding successively isolated and dominating vertices.
A threshold graph is uniquely determined by its degree sequence.
The Laplacian spectrum of a threshold graph is integral. Interpreting it as an integer partition, it is the conjugate of the partition given by its degree sequence.
Map
peak composition
Description
The composition corresponding to the peak set of a standard tableau.
Let $T$ be a standard tableau of size $n$.
An entry $i$ of $T$ is a descent if $i+1$ is in a lower row (in English notation), otherwise $i$ is an ascent.
An entry $2 \leq i \leq n-1$ is a peak, if $i-1$ is an ascent and $i$ is a descent.
This map returns the composition $c_1,\dots,c_k$ of $n$ such that $\{c_1, c_1+c_2,\dots, c_1+\dots+c_k\}$ is the peak set of $T$.
Map
reading tableau
Description
Return the RSK recording tableau of the reading word of the (standard) tableau $T$ labeled down (in English convention) each column to the shape of a partition.