Bug in step_response() #374

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1. bnavigator commented on Feb 20, 2020

   

   bnavigator

   on Feb 20, 2020

   Contributor

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   Can reproduce (with a different Exception raised). Properly formatted (Use the "insert code" function of github when posting code:

   In [1]: import control
   
   In [2]: u = control.TransferFunction([1],[1])
   
   In [3]: u
   Out[3]: 
   
   1
   -
   1
   
   
   In [4]: t, y = control.step_response(u)
   ---------------------------------------------------------------------------
   ValueError                                Traceback (most recent call last)
   <ipython-input-4-7a899e9160fd> in <module>
   ----> 1 t, y = control.step_response(u)
   
   /usr/lib/python3.7/site-packages/control/timeresp.py in step_response(sys, T, X0, input, output, transpose, return_x, squeeze)
       514     if T is None:
       515         if isctime(sys):
   --> 516             T = _default_response_times(sys.A, 100)
       517         else:
       518             # For discrete time, use integers
   
   /usr/lib64/python3.7/site-packages/scipy/signal/ltisys.py in _default_response_times(A, n)
      2056     # TODO: This could use some more work.
      2057     # For example, what is expected when the system is unstable?
   -> 2058     vals = linalg.eigvals(A)
      2059     r = min(abs(real(vals)))
      2060     if r == 0.0:
   
   /usr/lib64/python3.7/site-packages/scipy/linalg/decomp.py in eigvals(a, b, overwrite_a, check_finite, homogeneous_eigvals)
       767     return eig(a, b=b, left=0, right=0, overwrite_a=overwrite_a,
       768                check_finite=check_finite,
   --> 769                homogeneous_eigvals=homogeneous_eigvals)
       770 
       771 
   
   /usr/lib64/python3.7/site-packages/scipy/linalg/decomp.py in eig(a, b, left, right, overwrite_a, overwrite_b, check_finite, homogeneous_eigvals)
       231     lwork = _compute_lwork(geev_lwork, a1.shape[0],
       232                            compute_vl=compute_vl,
   --> 233                            compute_vr=compute_vr)
       234 
       235     if geev.typecode in 'cz':
   
   /usr/lib64/python3.7/site-packages/scipy/linalg/lapack.py in _compute_lwork(routine, *args, **kwargs)
       804     """
       805     dtype = getattr(routine, 'dtype', None)
   --> 806     ret = routine(*args, **kwargs)
       807     if ret[-1] != 0:
       808         raise ValueError("Internal work array size computation failed: "
   
   ValueError: On entry to DGEEV parameter number 5 had an illegal value
   
   In [5]: 
   

   👍React with 👍1Reacted by Rajab Legnain
2. bnavigator commented on Feb 20, 2020

   

   bnavigator

   on Feb 20, 2020

   Contributor

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   sys.A is empty for a unit TransferFunction

   👍React with 👍1Reacted by Rajab Legnain
3. ilayn commented on Feb 20, 2020

   

   ilayn

   on Feb 20, 2020

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   It's on my to do list to improve scipy.linalg.eig API for 1.5. 0. This shouldn't have happened regardless of the control issue and the error should have been raised from eig.

   I'll add an issue on the scipy side.
4. murrayrm commented on Feb 21, 2020

   

   murrayrm

   on Feb 21, 2020

   Member

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   At the same time, step_response probably shouldn't be computing default response times for an empty matrix (or _default_response_times should handle as a special case).

   👍React with 👍2Reacted by Ben Greiner and Rajab Legnain
5. murrayrm

   self-assigned this

   on Feb 21, 2020
6. murrayrm

   added

   bug

   on Feb 21, 2020
7. murrayrm

   linked a pull request that will close this issuefix computation of default response time for constant systems #383on Mar 22, 2020
8. murrayrm

   closed this as completedin #383on May 17, 2020