Gordon Royle on Fri, 01 Dec 2023 03:43:21 +0100

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Eigenvalues of symmetric matrices



I am using Pari/GP to compute the eigenvalues of a large number (10s of millions) of symmetric 0/1-matrices of order about 24 x 24 to 30 x 30; the matrices are adjacency matrices of 3-regular graphs and so have exactly three 1s per row and column.


At the moment, I am just using polrootsreal(charpoly(a)), but I wonder if there is a faster way to do it?