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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"StateSpace constructor should not call _remove_useless_states","articleBody":"State space representations should, in my opinion, not be reduced automatically with StateSpace._remove_useless_states(), similar to the fact that we don't call minreal() automatically.\r\n\r\nUnlike transfer functions, state space models can model non-observable or non-controllable behaviour, and cannot always be considered equivalent to their minimized form. Additionally, it is rather confusing to have `ss(A,B,C,D).A !== A`  and e.g. `ss(A,B,C,D).sample(T).A !== expm(A*T)`. For a more object-oriented interface, it would also be great to have member functions like stateSpace.isControllable(), which do not make sense if the system has already been minimized.\r\n\r\nTo give an example: The autonomous system x'=0, y=x  is a signal model for the constant output y=x(0). It is not equivalent to the system y=0 if you consider the initial response for x(0) !== 0.\r\n\r\n```\r\n​import control\r\nprint(control.__version__)\r\nprint(control.ss(0,0,1,0)) # expected: A,B,C,D unchanged from input\r\nprint(control.ss(0,0,1,0).sample(1)) # expected: ss(1,0,1,0, dt=1)\r\n```\r\noutput:\r\n```\r\n0.8.0\r\n\r\nA = []\r\nB = []\r\nC = []\r\nD = [[0]]\r\n\r\nA = []\r\nB = []\r\nC = []\r\nD = [[0]]\r\ndt = 1\r\n```\r\n\r\nIs there a reason for the current behavior, or would it be okay to change it?","author":{"url":"https://github.com/MaxGaukler","@type":"Person","name":"MaxGaukler"},"datePublished":"2018-11-14T10:55:53.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":8},"url":"https://github.com/244/python-control/issues/244"}