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gain offset using control.matlab.c2d using method='matched' ? #950
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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?
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
- linked a pull request that will close this issueFix bug in matched transformation + address other issues in #950 #951
on Dec 26, 2023 - added a commit that references this issue
on Dec 26, 2023 - added a commit that references this issue
on Aug 9, 2026
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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?