Description

murrayrm

opened on Jan 19, 2022

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If you pass the interconnect function a string instead of a list, it treats the string as a list (of characters). For example:

P1 = ct.rss(2, 1, 1)
P1_iosys = ct.LinearIOSystem(P1, inputs='u1', outputs='y1')
P2 = ct.rss(2, 1, 1)
P2_iosys = ct.LinearIOSystem(P2, inputs='y1', outputs='y2')
P_series = ct.interconnect([P1_iosys, P2_iosys], inputs=['u1'], outputs=('y2'))

generates the following error:

ValueError: could not find signal y

The problem appears to be that ('y2') is the same as 'y2' in Python and is being interpreted as ['y', '2']. Changing this to outputs=('y2',) or outputs=['y2'] fixes the problem, but it is still a bug.

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1. roryyorke

   added a commit that references this issue on Jan 29, 2022

   Interpret str-type args to `interconnect` as non-sequence

   This issue will close once commit 37d3148 is merged into the 'master' branch.

   37d3148
2. roryyorke commented on Jan 29, 2022

   

   roryyorke

   on Jan 29, 2022

   Contributor

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   This is easy enough to fix (I hope!), see PR.

   Two remarks: first, this description of the inputs arg mentions an option of an integer count, which I found difficult to understand, and which also doesn't seem to work:

       inputs : int, list of str or None, optional
           Description of the system inputs.  This can be given as an integer
           count or as a list of strings that name the individual signals.  If an
           integer count is specified, the names of the signal will be of the
           form `s[i]` (where `s` is one of `u`, `y`, or `x`).  If this parameter
           is not given or given as `None`, the relevant quantity will be
           determined when possible based on other information provided to
           functions using the system.
   

   My test case:

   In [26]: P1 = ct.LinearIOSystem(ct.rss(2,1,1), inputs='u1', outputs='y1')
       ...: P2 = ct.LinearIOSystem(ct.rss(2,1,1), inputs='y1', outputs='y2')
       ...: ct.interconnect([P1, P2], inputs=1)
       ...: 
   ---------------------------------------------------------------------------
   TypeError                                 Traceback (most recent call last)
   <ipython-input-26-ca5ff6a9552e> in <module>
         1 P1 = ct.LinearIOSystem(ct.rss(2,1,1), inputs='u1', outputs='y1')
         2 P2 = ct.LinearIOSystem(ct.rss(2,1,1), inputs='y1', outputs='y2')
   ----> 3 ct.interconnect([P1, P2], inputs=1)
   
   ~/src/python-control/control/iosys.py in interconnect(syslist, connections, inplist, outlist, inputs, outputs, states, params, dt, name, check_unused, ignore_inputs, ignore_outputs, **kwargs)
      2530     if not outlist and outputs is not None:
      2531         outlist = list(outputs)
   -> 2532 
      2533     # Process input list
      2534     if not isinstance(inplist, (list, tuple)):
   
   TypeError: 'int' object is not iterable
   

   Second, InterconnectedSystem refers one to interconnect for explanation of arguments, but while they're similar, I don't think they're identical; e.g., substituting InterconnectedSystem for interconnect in the example above doesn't work; one needs the actual system names (sys[0], etc.). I didn't look for other possible differences.
3. murrayrm

   closed this as completedin #698on Jan 30, 2022
4. murrayrm

   added a commit that references this issue on Mar 18, 2022

   Interpret str-type args to `interconnect` as non-sequence

   This issue will close once commit fdd2ecb is merged into the 'main' branch.

   fdd2ecb

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