Description

murrayrm

opened on Jan 18, 2021

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As described in issue #459 and PR #498, there are a number of type conversions for various overloaded operators that are not yet implemented. A table of the current and desired operations can be found in control/tests/type_conversion_test.py.

A few of the more useful ones:

• SISO StateSpace objects should be allowed to serve as a quotient under appropriate circumstances (so that you can write things like T = P*C/(1 + P*C) with state space objects, as you currently can with transfer functions.
• FrequencyResponseData and InputOutputSystem objects should be able to interact with floats and arrays.
• InputOutputSystem objects should be able to interact with LTI systems by converting the LTI system into a LinearIOSystem.
• FrequencyResponseData systems should be able to be combined with StateSpace and TransferFunction options by evaluating the state space system or transfer function at the FRD frequencies.

Reacted by Sawyer Fuller and Ben Greiner

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1. murrayrm

   added this to the 0.9.x milestone on Jan 18, 2021
2. sawyerbfuller commented on Feb 11, 2021

   

   sawyerbfuller

   on Feb 11, 2021

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   (this was originally its own issue, #541, but I copied the comment into here and closed that issue to keep discussion about its possible implementation in this more general thread.)

   The following code causes a bug when it tries to raise an error:

   import control as ct
   import control.iosys as io
   2*io.ss2io(ct.ss(1,1,1,1))

   raise NotImplemented("Scalar multiplication not yet implemented")

   This is because InputOutputSystems define various methods, e.g. __mul__ that override those in StateSpace and some are not implemented yet.

   Options that come to mind if we want this to work better:

   1. Test for instances of StateSpace correctly and dispatch. This seems to be onerous and at odds with how inheritance ought to make things easier.
   2. In the __init__ method of LinearIOSystem, delete those methods
   3. move those operations to NonLinearIOSystem (and override as necessary in LinearIOSystem when it makes sense to create a new LinearICSystem)

   Related: many of the methods like __mul__ don't act on self and other but rather sys1 and sys2. This might still work, but I think the first argument should be self according to Python convention.
3. murrayrm commented on Dec 30, 2021

   

   murrayrm

   on Dec 30, 2021

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   A number of these conversions have been implemented in #672. Leaving this issue open since there are still a few cases that aren't handled (see table in tests/type_conversion_test.py).
4. murrayrm

   removed this from the 0.9.1 milestone on Dec 30, 2021

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