The twelfth root of a matrix

[Gribouillis]

Yes I should have used np.allclose(A, la.matrix_power(B, 12)) to check the difference. That said it remains the issue that the matrix B is not unique and it would also be a good idea to use the fact that the third row is 0 0 1. If you have code that tries to do this, you can post it here for further discussion.