René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"TimeResponseData.to_pandas() fails if there are no states in a NonlinearIOSystem","articleBody":"TimeResponseData.to_pandas() fails if there are no states in a NonlinearIOSystem:\r\n\r\n```python\r\n\r\nimport control as ct\r\n\r\nclass System:\r\n    @classmethod\r\n    def _outputs(cls, t, x, u, params: dict):\r\n        v = u[0]\r\n        i = u[1]\r\n        k = u[2]\r\n\r\n        return k*v**2 + i\r\n\r\n    @classmethod\r\n    def build(cls):\r\n        return ct.NonlinearIOSystem(\r\n            None,\r\n            cls._outputs,\r\n            name=\"system\",\r\n            states=None,\r\n            inputs=('v', 'i', 'V'),\r\n            outputs=('I',),\r\n            params=params,\r\n        )\r\n\r\nT = np.arange(100)   # simulation time in seconds\r\nU = np.ones(shape=(3, len(T)))\r\n\r\nsys = System.build()\r\nydata = ct.input_output_response(sys, T=T, U=U, solve_ivp_method=\"Radau\").to_pandas()\r\n\r\n---------------------------------------------------------------------------\r\nTypeError                                 Traceback (most recent call last)\r\nCell In[106], [line 28](vscode-notebook-cell:?execution_count=106\u0026line=28)\r\n     [25](vscode-notebook-cell:?execution_count=106\u0026line=25) U = np.ones(shape=(3, len(T)))\r\n     [27](vscode-notebook-cell:?execution_count=106\u0026line=27) sys = System.build()\r\n---\u003e [28](vscode-notebook-cell:?execution_count=106\u0026line=28) ydata = ct.input_output_response(sys, T=T, U=U, solve_ivp_method=\"Radau\").to_pandas()\r\n     [29](vscode-notebook-cell:?execution_count=106\u0026line=29) ydata\r\n\r\nFile [~/workspace_TCC/repo_2022_2/.env/lib/python3.10/site-packages/control/timeresp.py:655](https://file+.vscode-resource.vscode-cdn.net/home/joaoantoniocardoso/workspace_TCC/repo_2022_2/models/2020/panel/~/workspace_TCC/repo_2022_2/.env/lib/python3.10/site-packages/control/timeresp.py:655), in TimeResponseData.to_pandas(self)\r\n    [650](https://file+.vscode-resource.vscode-cdn.net/home/joaoantoniocardoso/workspace_TCC/repo_2022_2/models/2020/panel/~/workspace_TCC/repo_2022_2/.env/lib/python3.10/site-packages/control/timeresp.py:650) data.update(\r\n    [651](https://file+.vscode-resource.vscode-cdn.net/home/joaoantoniocardoso/workspace_TCC/repo_2022_2/models/2020/panel/~/workspace_TCC/repo_2022_2/.env/lib/python3.10/site-packages/control/timeresp.py:651)     {name: self.u[i] for i, name in enumerate(self.input_labels)})\r\n    [652](https://file+.vscode-resource.vscode-cdn.net/home/joaoantoniocardoso/workspace_TCC/repo_2022_2/models/2020/panel/~/workspace_TCC/repo_2022_2/.env/lib/python3.10/site-packages/control/timeresp.py:652) data.update(\r\n    [653](https://file+.vscode-resource.vscode-cdn.net/home/joaoantoniocardoso/workspace_TCC/repo_2022_2/models/2020/panel/~/workspace_TCC/repo_2022_2/.env/lib/python3.10/site-packages/control/timeresp.py:653)     {name: self.y[i] for i, name in enumerate(self.output_labels)})\r\n    [654](https://file+.vscode-resource.vscode-cdn.net/home/joaoantoniocardoso/workspace_TCC/repo_2022_2/models/2020/panel/~/workspace_TCC/repo_2022_2/.env/lib/python3.10/site-packages/control/timeresp.py:654) data.update(\r\n--\u003e [655](https://file+.vscode-resource.vscode-cdn.net/home/joaoantoniocardoso/workspace_TCC/repo_2022_2/models/2020/panel/~/workspace_TCC/repo_2022_2/.env/lib/python3.10/site-packages/control/timeresp.py:655)     {name: self.x[i] for i, name in enumerate(self.state_labels)})\r\n    [657](https://file+.vscode-resource.vscode-cdn.net/home/joaoantoniocardoso/workspace_TCC/repo_2022_2/models/2020/panel/~/workspace_TCC/repo_2022_2/.env/lib/python3.10/site-packages/control/timeresp.py:657) return pandas.DataFrame(data)\r\n\r\nTypeError: 'NoneType' object is not iterable\r\n```\r\n\r\nNot optimal, but as a workaround, I'm introducing a state:\r\n\r\n```python\r\nclass System:\r\n    @classmethod\r\n    def _updates(cls, t, x, u, params: dict):\r\n        return 0\r\n\r\n    @classmethod\r\n    def _outputs(cls, t, x, u, params: dict):\r\n        v = u[0]\r\n        i = u[1]\r\n        k = u[2]\r\n\r\n        return k*v**2 + i\r\n\r\n    @classmethod\r\n    def build(cls):\r\n        return ct.NonlinearIOSystem(\r\n            cls._updates,\r\n            cls._outputs,\r\n            name=\"system\",\r\n            states=1,\r\n            inputs=('v', 'i', 'V'),\r\n            outputs=('I',),\r\n            params=params,\r\n        )\r\n```","author":{"url":"https://github.com/joaoantoniocardoso","@type":"Person","name":"joaoantoniocardoso"},"datePublished":"2024-01-03T18:02:54.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/957/python-control/issues/957"}