gain offset using control.matlab.c2d using method='matched' ?

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?

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

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

Fixed in #951. New plot:

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

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

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gain offset using control.matlab.c2d using method='matched' ? #950

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gain offset using control.matlab.c2d using method='matched' ? #950

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sawyerbfuller commented on Dec 25, 2023

murrayrm commented on Dec 26, 2023

murrayrm commented on Dec 26, 2023

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