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

[Ryan K. <kra...@gv...>]

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