Does this:
Run the AddUIPanel.py script in the text editor of the example .blend file -- then use the magnetic lines panel added to the object properties (object properties is the cube icon amongst the buttons screen-division, as shown in the screenshot above). To use with a new blender project, open all the .py files in the text editor, then run AddUIPanel.py to add the magnetic lines panel to the object properties.
The math is not the scientifically accurate math for magnets. This project is primarily just for visualization. The project just uses the inverse square law. I learned after making the project that it would probably be more appropriate if it used the inverse cube law.