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hvandonge opened this issue Aug 1, 2019 · 12 comments
Closed

How to use control.InputOutputSystem? #333

hvandonge opened this issue Aug 1, 2019 · 12 comments

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@hvandonge
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hvandonge commented Aug 1, 2019 •
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How do I actually start using control.InputOutputSystem?
I cannot do import control.InputOutputSystem, or from control import InputOutputSystem, or alike.
Can you please expand the documentation to include some of those basics? I am stuck at the start...

What I want to achieve is the following (from Matlab):

bypass = ss(eye(2),...
    'InputName',{'coll' 'long'},...
    'OutputName',{'coll' 'cycl_l'});
          
bypass_connect = parallel(ss_scas, bypass, 'name');
oloop = series(bypass_connect, model.ss, 'name');

% oloop = series(ss_scas, model.ss);
outputnames = {'u' 'w' 'tht' 'q' 'fx' 'fz' 'qdot'};
oloop.OutputName = outputnames;

FeedbackChannels = {'tht' 'q'};
K = ss(eye(2),'InputName',FeedbackChannels,...
              'OutputName',FeedbackChannels);
cloop = feedback(oloop,K,'name',+1);

ch47 = struct();
ch47.ss = cloop;
ch47.ss_red = minreal(cloop);

I suspect that the class mentioned above will be necessary for this to work. Or is there a work-around?
@murrayrm
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murrayrm commented Aug 1, 2019

A couple of comments:

  • For the example above, you are doing everything with linear systems => not necessary to use the control.iosys module (which was intended primarily for nonlinear systems). Note, however, that the current StateSpace class does not us named signals, so you have to use the control.connect function. See issue Elegant way to generate a transfer function matrix #325 for some related discussion.

  • One thing that won't work with the InputOutputSystems class is carrying out linear analysis operations (like minreal). Instead, you would have to construct the system (using commands like the ones that you have) and the linearize it to get a StateSpace system (which you could then pass to control.minreal).

  • An example of how to use the control.iosys module is in the examples directory, if you have the source code. Here is a direct link:

    https://github.com/python-control/python-control/blob/master/examples/steering-gainsched.py

I'll put on my list to put the key information into the online documentation. Hopefully the info above helps you get started.

@hvandonge
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Thank you for the response.
Tomorrow I will take a better look, but at first glance, regarding your last point, I get the following result:

system = ct.NonlinearIOSystem()
AttributeError: module 'control' has no attribute 'NonlinearIOSystem'

What is causing that?

If I understand correctly, I am better off using the connect method in combination with indexing.
And if I really want the I/O named signals, use iosys and convert it to a StateSpace.

Again, thanks a lot!

@murrayrm
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murrayrm commented Aug 1, 2019

Are you using the code from the master branch (via git)? The iosys module hasn't officially been released yet.

Try printing control.__version__ and see what that says. If you get 0.8.2, you are using the latest release but that doesn't have the iosys module.

@hvandonge
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That explains a lot, I am using 0.8.2.
In that case I will try with control.connect. Any idea when the new module will be released?

@murrayrm
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murrayrm commented Aug 2, 2019

I'll try to push something out in the next week or two. There are a couple of things to fix in issues #329 and #332, but then it should be good to go.

Out of curiosity, where did you see the information on the iosys module? If that is in any of the "default" online documentation about the package, we need to fix things up so that people don't try to access features that aren't yet avaliable.

@hvandonge
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hvandonge commented Aug 2, 2019 •
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Nice, I would quite like to use it (but I am not sure how to install the non-published version, and I don't know yet if I want to ;-)).

I read about it in https://python-control.readthedocs.io/en/latest/index.html under header Library Conventions and Control system classes, as I was really looking to find named connections.
Edit: In my eyes 0.8.2 was the same as latest, so I didn't get that those functionalities were not yet implemented in my version.

One question tho, if you don't mind, about the control.connect method. Is it only usable for feedback blocks? I want a few signals to bypass a controller, and add them subsequently to the output of the controller, is that something one can do with connect?

@murrayrm
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murrayrm commented Aug 2, 2019 •
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The control.connect function restricts the outputs to be the outputs of the subsystems you are connecting, so it probably won't work quite as you like. However, you can create some "feedthrough" blocks that let you do this. See this post for an example of how to do that.

@zgh551
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zgh551 commented Dec 20, 2019

My control library version is 0.8.2，but the AttributeError: module 'control' has no attribute 'NonlinearIOSystem'still hapen.i can open the iosys.py file and find the NonlinearIOSystem class.what's the question of my phenomenon

@murrayrm
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Theiosys module is not part of python-control 0.8.2. If you want to use that module, you need to either install from source or wait version 0.8.3 is released.

Note that just downloading the source code, where you will see iosys.py is not the same as installing it.

@zgh551
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zgh551 commented Dec 23, 2019

thank for your answer ,before i used conda install the python-control 0.8.2,so the python-control do not include the iosys file in conda.so i pull the github depository and using python install the python-control.By this way can generate the iosys file.

@murrayrm
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You may have a problem with your PYTHONPATH and you are not getting the right version. Try the following:

import control
print(control.__version__)

If you are importing the latest version, you should get something like

0.8.2.post173

If you are not getting the post173 (or something like it) then you are not importing the latest version. (The reason that the version does not list as 0.8.3 is that this has not yet been released.)

@murrayrm
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The iosys module is now released pas part of v0.8.3 and the documentation has been updated to give more information. Closing.

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@murrayrm @zgh551 @hvandonge