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JonHowMIT

opened on Dec 24, 2023

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Compared results of
sysc = ct.TransferFunction([1, z], [1, p])
sysd = ct.matlab.c2d(sysc, Ts, method='bilinear')
sysd1 = ct.matlab.c2d(sysc, Ts, method='matched')

yields a sysd1 with a gain that is about 10x that of sysd - is that expected?

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1. sawyerbfuller commented on Dec 25, 2023

   

   sawyerbfuller

   on Dec 25, 2023

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   Hi John great to hear from you and happy holidays. Glad to see you are using or at the very least evaluating the library.

   The matched c2d is code I have never used before and it doesn’t look like we have a unit test for it, so there is a decent chance it is just a bug. Thanks for the report!

   One q - when you refer to gain, do you mean the DC gain of the two systems?
2. murrayrm commented on Dec 26, 2023

   

   murrayrm

   on Dec 26, 2023

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   I did a quick check and I agree there is something wrong in the matched transformation:

   import control as ct
   sysc = ct.tf([1, 2], [1, 3], name='sysc')
   sysd_bilinear = ct.sample_system(sysc, 0.1, method='bilinear', name='sysd_bilinear')
   sysd_matched = ct.sample_system(sysc, 0.1, method='matched', name='sysd_matched')
   ct.bode([sysd_bilinear, sysd_matched, sysc])
   

   This produces the following plot:
   

   A couple of things to fix:

   • Zero frequency gain for the 'matched' transformation is incorrect.
   • The name of the system is lost when doing the 'matched' transformation.
   • The order of the system names is incorrect in the figure title
3. murrayrm

   self-assigned this

   on Dec 26, 2023
4. murrayrm

   added 2 commits that reference this issue on Dec 26, 2023

   fix bug in matched transformation + address other issues in python-co…

   d07072f

   fix bug in matched transformation + address other issues in python-co…

   3fb1a51
5. murrayrm

   linked a pull request that will close this issueFix bug in matched transformation + address other issues in #950 #951on Dec 26, 2023
6. murrayrm commented on Dec 26, 2023

   

   murrayrm

   on Dec 26, 2023

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   Fixed in #951. New plot:

   
7. murrayrm

   closed this as completedon Dec 26, 2023
8. murrayrm

   added a commit that references this issue on Dec 26, 2023

   Merge pull request #951 from murrayrm/matched_bug-26Dec2023

   177d8b6
9. binggao1230

   added a commit that references this issue on Aug 9, 2026

   Fix matched c2d NaN for a pole or zero at the origin

   f80d990

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