Description

samlaf

opened on May 14, 2020

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Hi, I found a bug in InterconnectedSystem when connecting two systems with different dt, one of which is None. I believe the correct semantic is for the new system to take the dt of the non-None system, but the way it is implemented, the order of the systems matters.

import control as ct
sys1 = ct.tf2io(ct.tf('s'))
sys2 = ct.NonlinearIOSystem(lambda t,x,u: x, name='sys2', states=('x'), inputs=('u'))
ct.InterconnectedSystem((sys2,sys1))

This code works, but changing the order of sys1 and sys2, as in ct.InterconnectedSystem((sys1,sys2)) gives a bug:

TypeError Traceback (most recent call last)
in
2 sys1 = ct.tf2io(ct.tf('s'))
3 sys2 = ct.NonlinearIOSystem(lambda t,x,u: x, name='sys2', states=('x'), inputs=('u'))
----> 4 ct.InterconnectedSystem((sys1,sys2))

/usr/local/lib/python3.7/site-packages/control-0.8.3-py3.7.egg/control/iosys.py in init(self, syslist, connections, inplist, outlist, inputs, outputs, states, params, dt, name)
892 dt = sys.dt
893 elif dt != sys.dt:
--> 894 raise TypeError("System timebases are not compatible")
895
896 # Make sure number of inputs, outputs, states is given

TypeError: System timebases are not compatible

Activity

1. murrayrm

   added this to the 0.8.4 milestone on Jul 11, 2020
2. murrayrm

   added

   bug

   on Jul 11, 2020
3. murrayrm

   self-assigned this

   on Jul 11, 2020
4. bnavigator

   removed this from the 0.8.4 milestone on Aug 17, 2020
5. bnavigator

   linked a pull request that will close this issueDefault dt is 0 #431on Aug 17, 2020
6. bnavigator

   added this to the 0.9.0 milestone on Aug 17, 2020
7. bnavigator commented on Aug 17, 2020

   

   bnavigator

   on Aug 17, 2020

   Contributor

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   Fixed by #431, but that will likely have to wait until 0.9.0. Reassigning milestone.
8. bnavigator

   linked a pull request that will close this issueRebased #431: Default dt is 0 #490on Dec 31, 2020
9. murrayrm commented on Dec 31, 2020

   

   murrayrm

   on Dec 31, 2020

   Member

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   I checked and #490 (rebased #431) fixes the initial bug that was reported regarding mixed timebases.

   However, it uncovered another bug: the command sys1 = ct.tf2io(ct.tf('s')) tries to generate a state space system having transfer function s (differentiator). This is not possible since you state space systems always have proper transfer functions and s is not proper => it should generate an error.

   Leaving this bug open until this is fixed. I'll also update the title.
10. murrayrm

    changed the title [-]Bug in InterconnectedSystem[/-] [+]Bugs in InterconnectedSystem: different dt's [fixed] and non-proper TFs [open][/+] on Dec 31, 2020
11. murrayrm

    linked a pull request that will close this issuegenerate error for tf2ss of non-proper transfer function #492on Dec 31, 2020
12. bnavigator

    closed this as completedin #490on Dec 31, 2020
13. bnavigator

    reopened this on Dec 31, 2020
14. bnavigator

    closed this as completedin #492on Dec 31, 2020

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