text: #!/usr/bin/env python3
  # -*- coding: utf-8 -*-
  import pandas as pd
  import matplotlib.pyplot as plt
  from matplotlib.backends.backend_pdf import PdfPages
  
  def read_it(folder):
      df = pd.read_csv(folder+'/fort.9',delim_whitespace = True,
          names=["time","CFL","drag","tke","s","U","a"])
      df.drop(df.index[:3], inplace=True)
      return df
  
  for accel in [0.5,2.0]:
      for reynolds in [2,3,4]:
          folder = 'acc{:02d}_rey5e{:01d}'.format(int(10*accel),reynolds)
          df = read_it(folder)
          plt.plot(df.s,df.drag,label=folder)
  plt.xlabel('s/D')
  plt.ylabel('drag')
  plt.legend()
  plt.savefig('compare.png')
  