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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`solve_flat_ocp` and scalar `timepts`","articleBody":"flowing from gh-1101, which complains about the code in question,\n\n`solve_flat_ocp` argument `timepts` is advertised in the docstring as being allowed to be scalar:\n\n```\n    timepts : float or 1D array_like\n        The list of points for evaluating cost and constraints, as well as\n        the time horizon.  If given as a float, indicates the final time for\n        the trajectory (corresponding to xf)\n```\n\nbut this doesn't work:\n\n```python\nimport numpy as np\nimport control as ct\nimport control.flatsys as fs\n\nf = fs.LinearFlatSystem(ct.ss(ct.tf([1],[1,1])))\n\ndef terminal_cost(x, u):\n    return (x-5).dot(x-5)+u.dot(u)\n\ntraj1 = fs.solve_flat_ocp(f, [0, 1], x0=[23],\n                          terminal_cost=terminal_cost)\n\ntraj2 = fs.solve_flat_ocp(f, 1, x0=[23],\n                          terminal_cost=terminal_cost)\n\nteval = np.linspace(0,1,101)\n\nr1 = traj1.response(teval)\nr2 = traj2.response(teval)\n\nassert np.max(abs(r1.x-r2.x)) == 0\nassert np.max(abs(r1.u-r2.u)) == 0\nassert np.max(abs(r1.y-r2.y)) == 0\n```\n\nproduces with master @ ebff1259\n\n```\nTraceback (most recent call last):\n  File \"/home/rory/projects/pycontrol/pyflakes/flatbug2.py\", line 13, in \u003cmodule\u003e\n    traj2 = fs.solve_flat_ocp(f, 1, x0=[23],\n                              terminal_cost=terminal_cost)\n  File \"/home/rory/src/python-control/control/flatsys/flatsys.py\", line 725, in solve_flat_ocp\n    T0 = timepts[0] if len(timepts) \u003e 1 else T0\n                                             ^^\nUnboundLocalError: cannot access local variable 'T0' where it is not associated with a value\n```\n\nI think the fix is as below. Diff also removes `Tf`, which is not used in the function.  With this diff the test script runs with error.\n\n```diff\n@@ -721,8 +721,7 @@ def solve_flat_ocp(\n \n     # Process final time\n     timepts = np.atleast_1d(timepts)\n-    Tf = timepts[-1]\n-    T0 = timepts[0] if len(timepts) \u003e 1 else T0\n+    T0 = timepts[0] if len(timepts) \u003e 1 else 0\n \n     # Process keyword arguments\n     if trajectory_constraints is None:\n```\n","author":{"url":"https://github.com/roryyorke","@type":"Person","name":"roryyorke"},"datePublished":"2025-02-01T11:27:49.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/1110/python-control/issues/1110"}