ctrl-viz

A Python library for visualizing control systems using Bode and Nyquist plots with the python-control library.

• Bode Plots: Create magnitude and phase plots of transfer functions

  • Full Bode plots (magnitude + phase)
  • Magnitude-only plots
  • Phase-only plots
  • Support for dB/linear magnitude and deg/rad phase
  • Frequency in rad/s or Hz

• Nyquist Plots: Visualize frequency response in the complex plane

  • Unit circle overlay
  • Critical point (-1, 0) marking
  • Direction arrows

1. Clone the repository:

git clone https://github.com/j3f-me/ctrl-viz.git
cd ctrl-viz

2. Install dependencies:

pip install -r requirements.txt

3. Install the package in development mode:

pip install -e .

[optional] For development or when using the jupyter lab demo, install the package like this:

pip install -e ".[dev,lab]"

Or install directly:

pip install -e src/

import control
from ctrl_viz import bode_plot, nyquist_plot

# Create a transfer function (1 / (s^2 + 0.5 s + 1))
system = control.TransferFunction([1], [1, 0.5, 1])

# Create a Bode plot
fig, axes = bode_plot(system, title="My System")

# Create a Nyquist plot
fig, ax = nyquist_plot(system, title="Nyquist Diagram")

from ctrl_viz import bode_plot, bode_magnitude, bode_phase
import control
import numpy as np

# Create a transfer function
G = control.TransferFunction([1], [1, 1])

# Full Bode plot
fig, (mag_ax, phase_ax) = bode_plot(G)

# Magnitude only
fig, ax = bode_magnitude(G)

# Phase only
fig, ax = bode_phase(G)

# With custom options
omega = np.logspace(-3, 3, 1000)
fig, axes = bode_plot(G, omega=omega, dB=True, deg=True, Hz=False)

from ctrl_viz import nyquist_plot
import control

# Create a transfer function
G = control.TransferFunction([1], [1, 0.5, 1])

# Basic Nyquist plot
fig, ax = nyquist_plot(G)

# With custom options
fig, ax = nyquist_plot(G, title="My Nyquist Plot", unit_circle=True)

Creates a complete Bode plot with magnitude and phase.

Parameters:

• system: Transfer function or state-space model
• omega: Frequency range in rad/s (auto if None)
• dB: Plot magnitude in decibels (default: True)
• deg: Plot phase in degrees (default: True)
• Hz: Use Hz instead of rad/s (default: False)
• title: Plot title
• figsize: Figure size tuple
• grid: Show grid (default: True)

Returns: (fig, (mag_ax, phase_ax))

Creates a magnitude-only Bode plot.

Creates a phase-only Bode plot.

Creates a Nyquist plot.

Parameters:

• system: Transfer function or state-space model
• omega: Frequency range in rad/s (auto if None)
• title: Plot title
• figsize: Figure size tuple
• grid: Show grid (default: True)
• unit_circle: Draw unit circle (default: True)
• arrows: Show direction arrows (default: True)

Returns: (fig, ax)

See the examples/demo.ipynb notebook for detailed usage examples.

Run an interactive local web app to plot transfer functions without writing a Python script:

pip install -e ".[web]"
python run_web.py

Then open http://127.0.0.1:8050/ in your browser.

Enter a rational expression in s, for example 1/(s^2+0.5*s+1), choose Nyquist and/or Bode plots, and click Calculate. The input field validates syntax in real time; invalid expressions are highlighted in red with an error hint.

• Python 3.8+
• control
• scipy
• matplotlib
• pytest (for testing)

Run tests with pytest:

pytest tests/

MIT License