plot.py

import numpy as np

import matplotlib.pyplot as plt

# Try to match font used in document in which plot will be embedded.
# If you plan on presenting on screen and including in a paper, you may want
# to have two versions of the plot with different font sizes. Complicating matters
# is the fact that some journals use sans serif for web and serif in PDFs. 
# See also
#   https://stackoverflow.com/questions/8753835/how-to-get-a-list-of-all-the-fonts-currently-available-for-matplotlib
plt.rcParams.update({'font.size': 14, 'font.family': 'serif'})

fname = 'data/lines.npy'
print(f'Reading {fname}')
lines = np.load(fname)
print(f'Read {fname}')

# Here I've colored everything black because I don't think additional colors
# will add more clarity.
plt.plot(lines[0,:,:], lines[1,:,:], 'k')
plt.plot(lines[0,0,:], lines[1,0,:], 'k.')
earth = plt.Circle((0, 0), 1, color='k')
plt.gca().add_patch(earth)
plt.xlabel('y or L')
plt.ylabel('z', rotation=0) # If label is short, I rotate to make easier to read.
plt.axis('equal') # So the field lines are not distorted by non-unity aspect ratio.
plt.title('Field lines for a dipole')
plt.grid()

# Save PNG for copy/paste into PPT. Save SVG for viewing in browser. Save PDF
# Also if plot will be put into a LaTeX document.
plt.savefig('figures/field_lines.png', dpi=300)
plt.savefig('figures/field_lines.svg')
#plt.savefig('figures/field_lines.pdf')
print('Wrote figures/field_lines.{png,svg}')
#print('Wrote figures/field_lines.{png,svg}')

plt.show() # Needed if this script is executed from the command line.