GeezerVison

coverage: 94.969% (+0.001%) from 94.968% when pulling 5c23f1a on sawyerbfuller:connections into 42c6fb1 on python-control:main.

This looks very useful for sorting out what is connected to what. A couple of questions and comments:

• What happens if the list of systems is longer than 32 characters. Is there a way to either truncate the field (perhaps end in "...") or adjust the spacing variable to make sure that the table stays lined up?
• Is there a way to generate a warning if the system was not generated using common signal names?
• A more general functionality seems like it would be possible by looking through the connect_map, input_map, and output_map arrays, which describe how everything is connected.

As an experiment, I tried modifying the example above to use a more typical form with a reference input:

P = ct.ss(1,1,1,0, inputs='u', outputs='y')
C = ct.tf(10, [.1, 1], inputs='e', outputs='u')
sumblk = ct.summing_junction(inputs=['r', '-y'], outputs='e')
T = ct.interconnect([C, P, sumblk], inputs='r', outputs='y')
T.signal_table()

which gives

signal    | source                        | destination
--------------------------------------------------------------------------
e         | system 2                      | system 0                      
y         | system 1                      | output, system 2              
r         | input                         | system 2                      
u         | system 0                      | system 1      

That looks right to me, but it it might be nice to see the fact that y goes into system 2 (the summing junction) with a negative gain.

This looks very useful for sorting out what is connected to what. A couple of questions and comments:

* What happens if the list of systems is longer than 32 characters.  Is there a way to either truncate the field (perhaps end in "...") or adjust the `spacing` variable to make sure that the table stays lined up?

Right now it just breaks alignment. I think a good solution might be to add an elipsis as you suggest, and to allow the user to set the spacing parameter. update forthcoming.

* Is there a way to generate a warning if the system was not generated using common signal names?

* A more general functionality seems like it would be possible by looking through the `connect_map`, `input_map`, and `output_map` arrays, which describe how everything is connected.

On further thought, I would propose the following:

1. change the name of this function to be more generic, such as "connection_table", rather than "signal_table", allowing for a future PR that perhaps produces a different kind of table for explicitly-connected systems.
2. which would pave the way for a future PR geared toward explicitly-connected systems that perhaps uses those maps. OTOH I think that such interconnections might better be presented in a table that puts the system name first, followed by its input and output systems. Perhaps a flag could be added to to the InterconnectedSystem class, specifying whether it was connected implicitly or explicitly, and choose the table type based on that.
3. (edit) add in a warning for the time being

As an experiment, I tried modifying the example above to use a more typical form with a reference input:

P = ct.ss(1,1,1,0, inputs='u', outputs='y')
C = ct.tf(10, [.1, 1], inputs='e', outputs='u')
sumblk = ct.summing_junction(inputs=['r', '-y'], outputs='e')
T = ct.interconnect([C, P, sumblk], inputs='r', outputs='y')
T.signal_table()

which gives

signal    | source                        | destination
--------------------------------------------------------------------------
e         | system 2                      | system 0                      
y         | system 1                      | output, system 2              
r         | input                         | system 2                      
u         | system 0                      | system 1      

That looks right to me, but it it might be nice to see the fact that y goes into system 2 (the summing junction) with a negative gain.

Great. I agree this could be useful. Open to it going into a future PR? I am not sure this information is stored anywhere in the interconnectedSystem class: the negative sign appears as one of the elements in summing junction's D matrix.

@murrayrm I incorporated (most of) your suggested updates:

• function warns if connections were made explicitly
  • to do this, I added a field to InterconnectedSystem.connection_type that indicates how connections were made: 'explicit'-ly, 'implicit'-ly, or not at all (None)
• table adds an elipsis if any column gets too long; user can now specify column width. Example:

    P1 = ct.ss(1,1,1,0, inputs='u', outputs='y', name='Plant1')
    P2 = ct.tf(10, [.1, 1], inputs='e', outputs='y', name='Plant2')
    P3 = ct.tf(10, [.1, 1], inputs='x', outputs='y', name='Plant3')
    L = ct.interconnect([P1, P2, P3], inputs=['e', 'u', 'x'], outputs='y')
    L.connection_table(show_names=True, column_width=23)

signal    | source               | destination
--------------------------------------------------------
x         | input                | Plant3               
e         | input                | Plant2               
u         | input                | Plant1               
y         | Plant1, Plant2, Pl.. | output               

• renamed function connection_table to make it more general, allowing for it to print a similar, but probably differently-formatted table for explicit connectiosn in the future
• I don't know of an obvious way to indicate negative connections. perhaps a future PR?