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Title: Add support for continuous delay systems by MythasNauveili · Pull Request #1148 · python-control/python-control · GitHub

Open Graph Title: Add support for continuous delay systems by MythasNauveili · Pull Request #1148 · python-control/python-control

X Title: Add support for continuous delay systems by MythasNauveili · Pull Request #1148 · python-control/python-control

Description: This PR introduces initial support for linear time-invariant (LTI) systems with time delays in python-control, inspired by the capabilities of ControlSystems.jl package, and the InternalDelay.py script from Skogestad-Python. Key features Creation of delay sytems Systems with delays can now be intuitively constructed by multiplying a TransferFunction object with a delay(tau) object or an exp(-tau*s) expression: tf_delay = tf([1], [1,1]) * delay(2) # or s = tf("s") tf_delay = tf([1], [1,1]) * exp(-2*s) Underlying Representation: The approach utilizes Linear Fractional Transformations (LFT) with a PartitionedStateSpace representation (implemented in partitionedssp.py). The DelayLTI class (in delaylti.py) serves as the core object for these systems. Operations: Standard operations such as addition, multiplication, and feedback are supported for DelayLTI objects. Time and Frequency Responses: Time responses for delayed systems are computed by solving the underlying Delay Differential Equations (DDEs). Frequency responses are also supported. Retrocompatibility: Maintain retrocompatibility with existing functionalities. Implementation Details: DDE Solver: Time responses for delayed systems are computed by solving DDEs. After exploring alternatives, a custom DDE solver based on the Method of Steps, wrapping SciPy's solve_ivp, was implemented in dde.py. Accuracy Note: While this solver performs well for many cases, for stiff problems, it may require smaller step sizes for convergence compared to specialized DDE solvers (like those in ControlSystems.jl). In tested scenarios, the error typically remains at least three orders of magnitude below the system response with reasonable step sizes. (An error estimation algorithm could be a valuable future addition). Validation: A Julia script (control/julia/compute_tests.jl) using ControlSystems.jl has been added to generate reference results, which are exported to a JSON file. These results are used in the test suite (control/tests/delay_lti_test.py and control/tests/dde_test.py) to benchmark the accuracy of the DelayLTI implementation and DDE solver. Current Scope and Limitations: This implementation currently focuses on continuous-time delay systems. Discrete-time delay systems are not yet covered. The DDE solver may benefit from further enhancements for stiff problems or adaptive step sizing. Discussion Points: This PR represents the initial groundwork for this feature. I'm submitting this draft to share these first steps and would appreciate feedback on: The overall approach and class design (DelayLTI, PartitionedStateSpace). The DDE solver implementation and its current performance. Any potential integration issues or API considerations. I'm aware there is still work to be done for this feature to be ready for a full release, but I believe this provides a solid foundation.

Open Graph Description: This PR introduces initial support for linear time-invariant (LTI) systems with time delays in python-control, inspired by the capabilities of ControlSystems.jl package, and the InternalDelay.py s...

X Description: This PR introduces initial support for linear time-invariant (LTI) systems with time delays in python-control, inspired by the capabilities of ControlSystems.jl package, and the InternalDelay.py s...

Opengraph URL: https://github.com/python-control/python-control/pull/1148

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de5a61f implement delayLTI and PartionedStateSpace classes and first algorith… MythasNauveili Mar 26, 2025 https://github.com/python-control/python-control/pull/1148/commits/de5a61fbd7e9b49d0c994a00f0ead356cb02c475
848d763 Merge branch 'python-control:main' into dev-delay MythasNauveili Mar 26, 2025 https://github.com/python-control/python-control/pull/1148/commits/848d763fb5c16843f25b8d24da9206300407a5dd
2c74ca1 ongoing tests with julia notebooks, feedback bug solved MythasNauveili Mar 26, 2025 https://github.com/python-control/python-control/pull/1148/commits/2c74ca110edf0a83d8a6ddcee64b34509e28859a
b6c0cde mimo building of delay systems MythasNauveili Mar 28, 2025 https://github.com/python-control/python-control/pull/1148/commits/b6c0cdeaa69405a1590383bb4b6ef2644dc5d982
8dcab54 implementation of working frequency response for delayed siso system MythasNauveili Mar 29, 2025 https://github.com/python-control/python-control/pull/1148/commits/8dcab549ec36bda02d411ee12942b4a8086ec714
9b7b062 __call__ implementation to use lti frequency response function MythasNauveili Mar 30, 2025 https://github.com/python-control/python-control/pull/1148/commits/9b7b0624192862e93ce5b7eb97518fb5fa40b187
e8a197b delay systems handle freq plots (julia comparison ok). Time to work o… MythasNauveili Mar 30, 2025 https://github.com/python-control/python-control/pull/1148/commits/e8a197bd03649448f74dfe68fa5c8fa1b3ecb1a7
29081b5 add dde.py file to improve readibility in timeresp.py MythasNauveili Mar 31, 2025 https://github.com/python-control/python-control/pull/1148/commits/29081b598155750cf16215d5e272656560e122d5
8f43ab9 add tests and docstrings, tests are all passing. ToDo: refine tests, … MythasNauveili Mar 31, 2025 https://github.com/python-control/python-control/pull/1148/commits/8f43ab9cb693e2d225d67b5dd8657481681a3997
30c05b9 improve tests by scripting julia code to mimic python tests, and seri… MythasNauveili Apr 3, 2025 https://github.com/python-control/python-control/pull/1148/commits/30c05b93e957442ac85f3a26a9207bf12bfe7690
53641f4 methods of steps implemented, 1E-5 accuracy against julia for first t… MythasNauveili May 1, 2025 https://github.com/python-control/python-control/pull/1148/commits/53641f4d5b1968cd79eeeec67c3f27dbceb8932e
b0f2cd3 Merge branch 'python-control:main' into dev-delay MythasNauveili May 3, 2025 https://github.com/python-control/python-control/pull/1148/commits/b0f2cd38d450681640d73c71e1ace355d32ecf65
4172ce8 cleaning old dde methods MythasNauveili May 3, 2025 https://github.com/python-control/python-control/pull/1148/commits/4172ce86f59c86d426d36fb7bf81b94e5dfa3c3d
a460513 mimo forced response passed. TODO: clean MythasNauveili May 9, 2025 https://github.com/python-control/python-control/pull/1148/commits/a4605137c07976e5721c28be0c941a25f709a709
f56e5de docstrings, ruff check and format MythasNauveili May 9, 2025 https://github.com/python-control/python-control/pull/1148/commits/f56e5de3b9abd9786362ea6636fcbb6db3dcf472
36ad284 improve formatting, underscore internal functions, add file description MythasNauveili May 12, 2025 https://github.com/python-control/python-control/pull/1148/commits/36ad284840875bba529e4a7afb569a883cd5555a
4870463 implement delay case in input_output_response, move and test issiso f… MythasNauveili May 12, 2025 https://github.com/python-control/python-control/pull/1148/commits/4870463ba2d6e128ce5baa6b847e7c084be49a63
1150646 remove forgotten debug print in timeresp, and unused imports in delay… MythasNauveili May 13, 2025 https://github.com/python-control/python-control/pull/1148/commits/115064642a3e8ac649981afeae8aa733c4d776c2
e9cf123 Merge branch 'python-control:main' into dev-delay MythasNauveili Aug 25, 2025 https://github.com/python-control/python-control/pull/1148/commits/e9cf123f6d29c8e4641fced343f2ff6096184386
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