From the following collection how to find only those graphs having only integer eigenvalue

asked 2019-07-04 16:43:29 +0100

Anonymous

updated 2019-07-11 18:57:37 +0100

for g in graphs.nauty_geng("8 -c"):

g.show()

h = g.laplacian_matrix().eigenvalues()

h.sort()

show(h)

I am trying to extract those graphs having all laplacian eigenvalues are integer. Is it possible to solve this problem in sage?

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Something like that

sage: [G for G in graphs(6) if all(f.degree()<=1 for f,d in G.charpoly().factor())]

FrédéricC ( 2019-07-05 09:11:13 +0100 )edit

ok. Can we see those graphs also having integer eigenvalues?

rewi ( 2019-07-05 13:24:54 +0100 )edit

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answered 2019-07-05 14:35:14 +0100

FrédéricC

5276 ●4 ●44 ●117

updated 2019-07-05 17:32:44 +0100

Like that

L = [G for G in graphs.nauty_geng("8 -c")
     if all(f.degree() <= 1 for f, d in G.laplacian_matrix().charpoly().factor())]

Then you have a list of graphs. You can then use

graphics_array([G.plot() for G in L])

or any other way to display them.

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Comments

But the output is not giving graphs. It is not coming correctly. When I run it on sage, the output is [Graph on 8 vertices, Graph on 8 vertices, Graph on 8 vertices, Graph on 8 vertices, Graph on 8 vertices, Graph on 8 vertices, Graph on 8 vertices, Graph on 8 vertices, Graph on 8 vertices, Graph on 8 vertices, Graph on 8 vertices, Graph on 8 vertices, Graph on 8 vertices, Graph on 8 vertices, Graph on 8 vertices, Graph on 8 vertices,

rewi ( 2019-07-05 15:45:45 +0100 )edit

Thanks a lot

rewi ( 2019-07-05 18:02:14 +0100 )edit

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From the following collection how to find only those graphs having only integer eigenvalue

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From the following collection how to find only those graphs having only integer eigenvalue