Using control.series to connect several discrete state-space systems, all with dt=0.05, is resulting in "ValueError:Systems have incompatible timebases" from "common_timebase" in namedio.py line 340 in release 0.9.2.

File "/usr/local/anaconda3/envs/c/lib/python3.9/site-packages/control/bdalg.py", line 108, in series return reduce(lambda x, y:y*x, sysn, sys1)

File "/usr/local/anaconda3/envs/c/lib/python3.9/site-packages/control/bdalg.py", line 108, in return reduce(lambda x, y:y*x, sysn, sys1)

File "/usr/local/anaconda3/envs/c/lib/python3.9/site-packages/control/iosys.py", line 184, in mul newsys = InterconnectedSystem(

File "/usr/local/anaconda3/envs/c/lib/python3.9/site-packages/control/iosys.py", line 895, in init dt = common_timebase(dt, sys.dt)

File "/usr/local/anaconda3/envs/c/lib/python3.9/site-packages/control/namedio.py", line 340, in common_timebase raise ValueError("Systems have incompatible timebases")

ValueError: Systems have incompatible timebases

In my case, the calling function init in iosys.py, line 895 is initializing "dt" as 0 from the global default then passing this as the first arg to common_timebase, while the second arg is the sys.dt from the first system in the list of systems being combined. This results in the ValueError. All systems in syslist have dt = 0.05 and pass common_timebase with each other when passed as args manually while stopped in debugger.

It seems like the intent for the object init functions in this module is probably that dt should be initialized as the dt of the first system in the syslist, but that is not what the code is doing.

As a work-around, running the same script with release 0.9.1 works.