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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Bugs in InterconnectedSystem: different dt's [fixed] and non-proper TFs [open]","articleBody":"Hi, I found a bug in InterconnectedSystem when connecting two systems with different dt, one of which is None. I believe the correct semantic is for the new system to take the dt of the non-None system, but the way it is implemented, the order of the systems matters.\r\n\r\n```\r\nimport control as ct\r\nsys1 = ct.tf2io(ct.tf('s'))\r\nsys2 = ct.NonlinearIOSystem(lambda t,x,u: x, name='sys2', states=('x'), inputs=('u'))\r\nct.InterconnectedSystem((sys2,sys1))\r\n```\r\nThis code works, but changing the order of sys1 and sys2, as in `ct.InterconnectedSystem((sys1,sys2))` gives a bug:\r\n\r\n\u003e TypeError                                 Traceback (most recent call last)\r\n\u003e \u003cipython-input-215-d3e121778200\u003e in \u003cmodule\u003e\r\n\u003e       2 sys1 = ct.tf2io(ct.tf('s'))\r\n\u003e       3 sys2 = ct.NonlinearIOSystem(lambda t,x,u: x, name='sys2', states=('x'), inputs=('u'))\r\n\u003e ----\u003e 4 ct.InterconnectedSystem((sys1,sys2))\r\n\u003e \r\n\u003e /usr/local/lib/python3.7/site-packages/control-0.8.3-py3.7.egg/control/iosys.py in __init__(self, syslist, connections, inplist, outlist, inputs, outputs, states, params, dt, name)\r\n\u003e     892                 dt = sys.dt\r\n\u003e     893             elif dt != sys.dt:\r\n\u003e --\u003e 894                 raise TypeError(\"System timebases are not compatible\")\r\n\u003e     895 \r\n\u003e     896             # Make sure number of inputs, outputs, states is given\r\n\u003e \r\n\u003e TypeError: System timebases are not compatible","author":{"url":"https://github.com/samlaf","@type":"Person","name":"samlaf"},"datePublished":"2020-05-14T02:15:08.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/399/python-control/issues/399"}