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DarioTurchi

opened on Jan 30, 2021

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Hello,
It seems to me that when I try to define a non-minimal state representation (e.g. with a state that can't be controlled or that doesn't have a dynamic) the system returned by the StateSpace class is automatically reduced, by eliminating such "non meaningful" states.
As example consider the following code:

from control import StateSpace

a = [[0., 0., 0.], [0., 0., 0.], [0., 0., 0.]]
b = [[1, 0], [0, 0], [0, 1]]
c = [[1, 0, 0], [0, 1, 0], [0, 0, 1]]
d = [[0, 0], [0, 0], [0, 0]]
x = StateSpace(a,b,c,d)

the obtained state representation is the following :

>>> x
A = [[0. 0.]
 [0. 0.]]

B = [[1. 0.]
 [0. 1.]]

C = [[1. 0.]
 [0. 0.]
 [0. 1.]]

D = [[0. 0.]
 [0. 0.]
 [0. 0.]]

where the second state has been removed. Is it possible to not have this automatic model reduction (regardless of the fact that such state is not meaningful ) ? I couldn't find anything in the documentation

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1. bnavigator commented on Jan 30, 2021

   

   bnavigator

   on Jan 30, 2021

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   Hello Dario,

   this has recently been fixed in #509. Until it lands in a release, you can manually set remove_useless_states=False:

   >>> from control.config import set_defaults
   >>> set_defaults('statesp', remove_useless_states=False)
   >>> x = StateSpace(a,b,c,d)
   >>> x
   StateSpace(array([[0., 0., 0.],
          [0., 0., 0.],
          [0., 0., 0.]]), array([[1., 0.],
          [0., 0.],
          [0., 1.]]), array([[1., 0., 0.],
          [0., 1., 0.],
          [0., 0., 1.]]), array([[0., 0.],
          [0., 0.],
          [0., 0.]]))
   
   
2. murrayrm

   added

   duplicate

   on Jan 30, 2021
3. murrayrm commented on Jan 30, 2021

   

   murrayrm

   on Jan 30, 2021

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   Closing since this has been fixed (also duplicates #244).
4. murrayrm

   closed this as completedon Jan 30, 2021
5. DarioTurchi commented on Jan 31, 2021

   

   DarioTurchi

   on Jan 31, 2021

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   @murrayrm @bnavigator
   I am really sorry to keep bothering you, but this is still not working for me.
   Do I need the package above a specific version (have 0.8.3)?
   Am I doing anything stupid ?

   I tried with both numpy array and lists for the definition of matrices A,B,C,D:

   Python 3.8.5 (default, Jul 28 2020, 12:59:40) 
   [GCC 9.3.0] on linux
   Type "help", "copyright", "credits" or "license" for more information.
   >>> import control as ctr
   >>> ctr.config.set_defaults('statesp', remove_useless_states=False)
   >>> a = [[0., 0., 0.], [0., 0., 0.], [0., 0., 0.]]
   >>> b = [[1, 0], [0, 0], [0, 1]]
   >>> c = [[1, 0, 0], [0, 1, 0], [0, 0, 1]]
   >>> d = [[0, 0], [0, 0], [0, 0]]
   >>> x = ctr.StateSpace(a,b,c,d)
   >>> ctr.config._get_param('statesp', 'remove_useless_states')
   False
   >>> x
   A = [[0. 0.]
    [0. 0.]]
   
   B = [[1. 0.]
    [0. 1.]]
   
   C = [[1. 0.]
    [0. 0.]
    [0. 1.]]
   
   D = [[0. 0.]
    [0. 0.]
    [0. 0.]]
   
   >>>
   

   Python 3.8.5 (default, Jul 28 2020, 12:59:40) 
   [GCC 9.3.0] on linux
   Type "help", "copyright", "credits" or "license" for more information.
   >>> from numpy import array
   >>> from control import StateSpace
   >>> from control.config import set_defaults, _get_param
   >>> a = array([[0., 0., 0.], [0., 0., 0.], [0., 0., 0.]])
   >>> b = array([[1, 0], [0, 0], [0, 1]])
   >>> c = array([[1, 0, 0], [0, 1, 0], [0, 0, 1]])
   >>> d = array([[0, 0], [0, 0], [0, 0]])
   >>> set_defaults('statesp', remove_useless_states=False)
   >>> x = StateSpace(a,b,c,d)
   >>> _get_param('statesp', 'remove_useless_states')
   False
   >>> x
   A = [[0. 0.]
    [0. 0.]]
   
   B = [[1. 0.]
    [0. 1.]]
   
   C = [[1. 0.]
    [0. 0.]
    [0. 1.]]
   
   D = [[0. 0.]
    [0. 0.]
    [0. 0.]]
   
   >>>
   

   The _get_param function correctly reports the considered setting as False, still getting a reduced model
6. sawyerbfuller commented on Jan 31, 2021

   

   sawyerbfuller

   on Jan 31, 2021 via email

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   Try remove_useless=False? (Leave out ‘states’) the constructor should raise an error if it receives an un-recognized keyword like this.
7. murrayrm commented on Jan 31, 2021

   

   murrayrm

   on Jan 31, 2021

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   Yes, in v0.8.3 the keyword was called remove_useless, so you have to use

   x = ctr.StateSpace(a,b,c,d, remove_useless=False)
   

   Note also that v0.8.3 did not use the config module to set the default value, so calling set_defaults won't work in that version.

   v0.8.4 changes the name of the keyword to remove_useless_states and sets the default value to True (but you can use set_defaults to override).

   v0.9.0 (upcoming) sets the default value to False.
8. DarioTurchi commented on Jan 31, 2021

   

   DarioTurchi

   on Jan 31, 2021

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   Many thanks

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