Re: [python-control-discuss] really weird error for SISO step response

[Murray, R. M. <mu...@cd...>]

Which version of python-control and slycot?  I just ran against the latest master and slycot 0.3.4 and it didn’t generate an error.

-richard

> On 29 Aug 2019, at 11:04 , Ryan Krauss <kra...@gv...> wrote:
> 
> I am trying to do a super basic step response for a first order TF and am getting an error I have never seen before.  The notebook is attached, but here is the code and the error message:
> 
> %matplotlib inline
> import matplotlib.pyplot as plt
> import numpy as np
> import control
> from numpy import sin, cos, tan, pi
> from control import TransferFunction as TF
> 
> p = 30
> 
> G = control.TransferFunction(p,[1,p])
> G
> 
> control.step_response(G)
> 
> ---------------------------------------------------------------------------
> ValueError
>                                 Traceback (most recent call last)
> 
> <ipython-input-7-7235fbf92fdd> in <module>()
> ----> 1 control.step_response(G)
> 
> 
> 
> /usr/local/lib/python3.6/site-packages/control/timeresp.py in step_response(sys, T, X0, input, output, transpose, return_x)
>     450     >>> T, yout = step_response(sys, T, X0)
>     451
>      """
> 
> --> 452     sys = _get_ss_simo(sys, input, output)
>     453     if T is None:
>     454         if isctime(sys):
> 
> 
> 
> /usr/local/lib/python3.6/site-packages/control/timeresp.py in _get_ss_simo(sys, input, output)
>     378     If input is not specified, select first input and
>  issue warning
> 
>     379
>      """
> 
> --> 380     sys_ss = _convertToStateSpace(sys)
>     381     if sys_ss.issiso():
>     382         return
>  sys_ss
> 
> 
> /usr/local/lib/python3.6/site-packages/control/statesp.py in _convertToStateSpace(sys, **kw)
>     895             # transfer function to state space conversion now should work!
>     896
>              ssout = td04ad('C', sys.inputs, sys.outputs,
> 
> --> 897
>                             denorder, den, num, tol=0)
> 
>     898
>  
> 
>     899             states = ssout[0]
> 
> 
> 
> /usr/local/lib/python3.6/site-packages/slycot/transform.py in td04ad(rowcol, m, p, index, dcoeff, ucoeff, tol, ldwork)
>     446         e = ValueError(error_text)
>     447         e.info = out[-1]
> --> 448         raise
>  e
> 
>     449     if out[-1] > 0:
>     450         error_text = "The leading coefficient of a denominator polynomial is nearly zero; calculations would overflow; no state-space representation was calculated. ABS(DCOEFF("+str(out[-1])+",1))="+str(abs(dcoeff(out[-1],1)))+" is too small."
> 
> 
> 
> ValueError: The following argument had an illegal value: dcoeff
> 
> --
> Dr. Ryan Krauss
> Associate Professor
> Product Design and Manufacturing Engineering
> Grand Valley State University
> <illegeal_dcoeff.ipynb>_______________________________________________
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