Obtaining a Lie algebra from a list of matrices

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Given a finite list W of nilpotent matrices in Sage. How can I obtain the Lie algebra L generated by those matrices in W? And how can I find the vector space dimension and test whether L is simple using Sage? I googled a bit and found the command:

L=LieAlgebra(associative=[M, N])

here [M,N] is a list of two matrices. It works to give me a Lie algebra, but then nearly no command works to find the dimension of L (I guess it is somehow in the wrong category?)