SymPy Control Package #412

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1. murrayrm commented on Jun 3, 2020

   

   murrayrm

   on Jun 3, 2020

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   Excellent! It would be great to "link" the two projects, in the sense that if there are good ideas from the SymPy project that we can pull into python-control that we keep track and do that. And definitely we would hope to be able to "project" controlsys models into python-control models by specifying parameter values, etc, at the appropriate point in time.
2. murrayrm commented on Jun 3, 2020

   

   murrayrm

   on Jun 3, 2020

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   Also, perhaps we keep this issue open as a way to share ideas about how the project is evolving and features we should be keeping track of.
3. murrayrm

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   on Jun 3, 2020
4. moorepants commented on Jun 3, 2020

   

   moorepants

   on Jun 3, 2020

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   @namannimmo10 See this issue. This will be a good way for you to connect with this project and share some ideas and questions.

   👍React with 👍1Reacted by Naman Gera
5. namannimmo10 commented on Jun 3, 2020

   

   namannimmo10

   on Jun 3, 2020

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   Amazing, he's the one who wrote python-control's Transfer Function class. :)
6. namannimmo10 commented on Jun 4, 2020

   

   namannimmo10

   on Jun 4, 2020

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   I have a question related to TransferFunction representation in python control.

   I understand that when the denominator polynomial becomes zero, the value of the transfer function becomes unbounded, and hence it should raise a ValueError.

   >>> from control import TransferFunction; s = TransferFunction.s
   >>> G = TransferFunction([2, 1, 0], [0]); G
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
     File "/home/dell/python-control/control/xferfcn.py", line 183, in __init__
       % (j + 1, i + 1))
   ValueError: Input 1, output 1 has a zero denominator.

   But when the numerator is zero, regardless of what the denominator is, the transfer function should vanish.. & here it sets the denominator to be equal to 1.

   >>> G = 0/(s**2 - s + 1); G
   
   0
   -
   1
   
   >>> type(G)
   <class 'control.xferfcn.TransferFunction'>

   Why is it designed this way?
7. murrayrm commented on Jun 4, 2020

   

   murrayrm

   on Jun 4, 2020

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   There are probably a couple of things going on (its been a while since that class was created):

   • If the numerator of a transfer function is zero, then the transfer function still needs to exist. But for every input, the output should be zero.
   • There are many equivalent transfer functions that can achieve this (for example, the original transfer function that you used or the transfer function given by 0/1).
   • There was probably a desire to use a "minimal" representation (fewest number of states), so this might have been the reason for setting the denominator to a constant (1 being the natural constant to use).

   There is some discussion about whether to automatically return minimal realizations in issue #244.

   If I were doing this again, I would probably leave the denominator along and just set the numerator to 0.
8. namannimmo10 commented on Jun 4, 2020

   

   namannimmo10

   on Jun 4, 2020

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   Thanks!

   If I were doing this again, I would probably leave the denominator along and just set the numerator to 0.

   OK, I'll do it this way.
9. Sc0rpi0n101 commented on Jun 5, 2020

   

   Sc0rpi0n101

   on Jun 5, 2020

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   Interested folks can also check out sympy/sympy#19352 to keep track of the progress of the package and the relevant PRs.

   I think you should add this issue to the OP too, Jason.
10. namannimmo10 commented on Jul 17, 2020

    

    namannimmo10

    on Jul 17, 2020

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    Hi @murrayrm!
    Here's the link to my second PR on MIMO transfer functions: sympy/sympy#19761
    You can share some ideas or suggestions when you have time! Thanks.
11. murrayrm

    closed this as completedon Mar 13, 2021
12. python-control

    locked and limited conversation to collaborators on Mar 13, 2021