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Checking Similarity of Matrices over Finite Fields

asked 2014-12-27 17:55:18 -0500

algebraicallyclosed gravatar image

updated 2016-11-21 04:54:25 -0500

tmonteil gravatar image

Hi, There is a command in SAGE which allows us to check the similarity of two matrices over Q (or sth); is_similar()

But, when trying to check two matrices' similarity over Finite Fields it usually gives the error: "unable to compute Jordan canonical form for matrix"

I would be appreciated if someone can help me to construct a practical way to check the similarity of two matrices with entries in Finite Fields.

Thanks in advance,

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answered 2014-12-28 01:28:21 -0500

FrédéricC gravatar image

The problem is that some eigenvalues do not lie in the finite field. This prevents the existence of the Jordan form. You need to extend coefficients.

sage: M = matrix(GF(13),[[4,6],[5,9]])
sage: M.jordan_form()
RuntimeError: Some eigenvalue does not exist in Finite Field of size 13.
sage: K = M.parent().base_ring()
sage: L = K.extension(M.minimal_polynomial(),'a')
sage: ML = M.change_ring(L)
sage: ML.jordan_form()
[12*a|   0]
[   0|   a]
sage: ML.is_similar(ML**2)
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Asked: 2014-12-27 17:55:18 -0500

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Last updated: Dec 28 '14