new_contents: import ucilib.Sim as Sim
  import ucilib.BorisUpdater as BorisUpdater
  import numpy as np
  
  
  # Some helpful constants.
  fund_charge = 1.602176565e-19
  
  
  # Mass of Be^+ ions.
  ion_mass = 8.9465 * 1.673e-27
  
  
  # Create a simulation with n particles.
  n = 10000
  s = Sim.Sim()
  s.ptcls.set_nptcls(n)
  
  
  # 1/e radius of cloud.
  s.ptcls.rmax = 2.0e-4
  s.ptcls.init_ptcls(charge = fund_charge, mass = ion_mass)
  
  
  # Turn the first n/2 particles into electrons by setting their mass and
  # charge.
  s.ptcls.q()[:(n/2)] = -fund_charge * np.ones(n/2)
  s.ptcls.m()[:(n/2)] = 9.1e-31 * np.ones(n/2)
  
  
  # Finally we set the updater.
  s.updater = BorisUpdater.BorisUpdater(s.ctx, s.queue)
  
  
  
subject: Add an example simulation setup for an ultracold neutral plasma.