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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"_remove_useless_states() can change types to ndarrays","articleBody":"It seems that if you enter the if statement [here](https://github.com/python-control/python-control/blob/master/control/statesp.py#L182-L186) then it replaces self.A with`self.A` with `zeros(1,1)` which is of type ndarray. This will cause problems later as the library is taking advantage of the fact that \\* is matrix multiplication not elementwise multiplcation as it would be for ndarrays. \n\nHere is an example of the problem\n\n``` python\nsys1 = control.StateSpace(0,0,0,0)\nsys2 = control.StateSpace(1,0,0,0)\nprint \"type(sys1.A)\", type(sys1.A)\nprint \"type(sys2.A)\", type(sys2.A)\n\n\ntype(sys1.A) \u003ctype 'numpy.ndarray'\u003e\ntype(sys2.A) \u003cclass 'numpy.matrixlib.defmatrix.matrix'\u003e\n```\n","author":{"url":"https://github.com/manuelli","@type":"Person","name":"manuelli"},"datePublished":"2016-04-07T00:51:03.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/82/python-control/issues/82"}