René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Possible bug: control.interconnect fails to construct a extended system with zero input and one output (D matrix shape mismatch)","articleBody":"## About the problem\n\n### Summary\nI attempted to simulate a control system with an output-feedback controller, defining a plant and a controller as subsystems.\nWhen using `control.interconnect` to connect these subsystems, an error occurs because an extended system obtained by connecting subsystems has zero input and one output.\nIs it impossible to define a system with zero input and one output using the `control.interconnect` function?\n\n\n### Error message \n```\ncontrol.exception.ControlDimension: Incompatible dimensions of D matrix; expected (1, 0) but found (0, 0)\n```\n\n\n\n### System information\n- OS: macOS Sonoma 14.3.1\n- Python: 3.12.2\n- python-control: 0.10.2\n\n\n\n### Cause of this problem\nWhen we set the inputs and outputs of the extended system as zero input and one input, the D matrix of the extended system has `(1, 0)` dimension.\nHowever, the dimension of D matrix is converted to `(0, 0)` dimension by `_ssmatrix` function at line 218 of `statesp.py`.\nAs a result, the mismatch of the dimensions occurs.\n(When we set both inputs and outputs to zero, the error does not occur.)\n\n\n\n\n\n## To reproduce the error\n```python\nimport numpy as np\nimport control as ct\n\ndef main():\n\n    # Define the coefficient matrices of plant P\n    A = np.array(\n        [\n            [1.00, 1.00],\n            [0.00, -2.0],\n        ]\n    )\n    B = np.array(\n        [\n            [0.00],\n            [1.00]\n        ]\n    )\n    C = np.array(\n        [\n            [1.00, 0.00]\n        ]\n    )\n\n    # Define the coefficient matrices of controller C\n    A_c = np.array(\n        [\n            [2.25, 1.00],\n            [-5.0, -0.5]\n        ]\n    )\n    B_c = np.array(\n        [\n            [-1.25],\n            [4.500]\n        ]\n    )\n    C_c = np.array(\n        [\n            [-0.50, 1.500]\n        ]\n    )\n\n    # Define the subsystems\n    P = ct.ss(\n        A,\n        B,\n        C,\n        np.zeros([C.shape[0], B.shape[1]]),\n        inputs=[f'u_p{i}' for i in range(B.shape[1])],\n        outputs=[f'y_p{i}' for i in range(C.shape[0])],\n        name='P',\n        dt=True\n    )\n    C = ct.ss(\n        A_c,\n        B_c,\n        C_c,\n        np.zeros([C_c.shape[0], B_c.shape[1]]),\n        inputs=[f'y_p{i}' for i in range(B_c.shape[1])],\n        outputs=[f'u_p{i}' for i in range(C_c.shape[0])],\n        name='C',\n        dt=True\n    )\n\n    sys = ct.interconnect(\n        [P, C],\n        inplist=None,\n        outlist=[f'y_p{i}' for i in range(P.C.shape[0])]\n    )\n\nif __name__ == '__main__':\n    main()\n```","author":{"url":"https://github.com/yuu5g0g0","@type":"Person","name":"yuu5g0g0"},"datePublished":"2025-07-27T06:35:44.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/1176/python-control/issues/1176"}