text: #! /usr/bin/env python
  
  # Copyright 2019 Luca Fedeli, Maxence Thevenet
  #
  # This file is part of WarpX.
  #
  # License: BSD-3-Clause-LBNL
  
  import yt
  import numpy as np
  import scipy.stats as st
  import sys
  
  # This script checks if photons initialized with Breit Wheeler process enabled
  # do actually have an exponentially distributed optical depth
  
  # Tolerance
  tol = 1e-2
  
  def check():
      filename = sys.argv[1]
      data_set = yt.load(filename)
  
      all_data = data_set.all_data()
      res_tau = all_data["photons", 'particle_tau']
  
      loc, scale = st.expon.fit(res_tau)
  
      # loc should be very close to 0, scale should be very close to 1
      assert(np.abs(loc - 0) < tol)
      assert(np.abs(scale - 1) < tol)
  
  def main():
      check()
  
  if __name__ == "__main__":
      main()
  
  