Any plan for step_info to support negative step responses?

I have step responses that go negative and sometimes stay negative, and it breaks the settling time calculation and rise time calculation. I've been messing around with it and might open a pull request if this is something y'all would be interested in.

For example, here is my code, the step response plot, and the error

from control import tf, step_response, step_info
import matplotlib.pyplot as plt
import numpy as np

transfer_function = tf( [3.32, 0, -162.8], [1, 24.56, 186.5, 457.8, 116.2] )
time, response = step_response(transfer_function)

fig, ax = plt.subplots(1, 1)
ax.plot(time, response)
plt.show()

step_info(transfer_function)

step_info() gives the following error

Traceback (most recent call last):
  File "bug_test.py", line 14, in <module>
    step_info(transfer_function)
  File "/Users/hgducharme/Programming/pendulum/env/lib/python3.7/site-packages/control/timeresp.py", line 536, in step_info
    SettlingTime = T[i + 1]
IndexError: index 1000 is out of bounds for axis 0 with size 1000

When I run this code in MATLAB, I get the following result

@joaoantoniocardoso

@joaoantoniocardoso Any interest in taking a look at this?

@murrayrm

@murrayrm Yes, I think I can take a look at this tomorrow.

Also I think this error is not something that happens only for negative step responses... Months ago I did a pull-request (#293 ) that fixes some cases with the same message. (That pull was closed because while fixes some cases, it breaks others)

Hi, think I solved this problem and the problem of systems with non settling time, I mean when dcgain isinf or isnan, doing:

    # Steady state value
    InfValue = sys1.dcgain()
    if InfValue < 0.0:
        yout = -yout
        InfValue = np.abs(InfValue)




    # SettlingTime
    sup_margin = (1. + SettlingTimeThreshold) * np.abs(InfValue)
    inf_margin = (1. - SettlingTimeThreshold) * np.abs(InfValue)
    # find Steady State looking for the first point out of specified limits
    if np.isnan(InfValue) or np.isinf(InfValue):
        SettlingTime = np.NaN
    else:
        for i in reversed(range(time.size-1)):
            if((np.abs(yout[i]) <= inf_margin) | (np.abs(yout[i]) >= sup_margin)):
                SettlingTime = T[i + 1]
                break

@juanodecc

Hi @juanodecc, it seems like a good solution. Could you open a PR with that, adding also a test case with a negative system and another with a system with non-settling time? Thanks

Solve issue python-control#337, python-control#565 and python-control…

Navigation Menu

Repository navigation

Any plan for step_info to support negative step responses? #337

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Any plan for step_info to support negative step responses? #337

Description

Activity

murrayrm commented on Aug 21, 2019

joaoantoniocardoso commented on Aug 21, 2019

juanodecc commented on Mar 9, 2021

joaoantoniocardoso commented on Mar 9, 2021

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions