docs: def main():
      """
      NAME
         common_mean.py
  
      DESCRIPTION
         calculates bootstrap statistics to test for common mean
  
      INPUT FORMAT
         takes dec/inc as first two columns in two space delimited files
     
      SYNTAX
         common_mean.py [command line options]
      
      OPTIONS
         -h prints help message and quits
         -f FILE, input file 
         -f2 FILE, optional second file to compare with first file
         -dir D I, optional direction to compare with input file
         -fmt [svg,jpg,pnd,pdf] set figure format [default is svg]
      NOTES
         must have either F2 OR dir but not both
       
  
      """
      d,i,file2="","",""
      fmt,plot='svg',0
      if '-h' in sys.argv: # check if help is needed
          print(main.__doc__)
          sys.exit() # graceful quit
      if '-sav' in sys.argv: plot=1
      if '-fmt'  in sys.argv:
          ind=sys.argv.index('-fmt')
          fmt=sys.argv[ind+1]
      if '-f' in sys.argv:
          ind=sys.argv.index('-f')
          file1=sys.argv[ind+1]
      if '-f2' in sys.argv:
          ind=sys.argv.index('-f2')
          file2=sys.argv[ind+1]
      if '-dir' in sys.argv:
          ind=sys.argv.index('-dir')
          d=float(sys.argv[ind+1])
          i=float(sys.argv[ind+2])
      D1=numpy.loadtxt(file1,dtype=numpy.float)
      if file2!="": D2=numpy.loadtxt(file2,dtype=numpy.float)
  #
      counter,NumSims=0,1000
  #
  # get bootstrapped means for first data set
  #
      print("Doing first set of directions, please be patient..")
      BDI1=pmag.di_boot(D1)
  #
  #   convert to cartesian coordinates X1,X2, Y1,Y2 and Z1, Z2
  #
      if d=="": # repeat for second data set
          print("Doing second  set of directions, please be patient..")
          BDI2=pmag.di_boot(D2)
      else:
          BDI2=[]
  # set up plots
      CDF={'X':1,'Y':2,'Z':3}
      pmagplotlib.plot_init(CDF['X'],4,4)
      pmagplotlib.plot_init(CDF['Y'],4,4)
      pmagplotlib.plot_init(CDF['Z'],4,4)
  # draw the cdfs
      pmagplotlib.plot_com(CDF,BDI1,BDI2,[d,i])
      files={}
      files['X']='CD_X.'+fmt
      files['Y']='CD_Y.'+fmt
      files['Z']='CD_Z.'+fmt
      if plot==0:
          pmagplotlib.draw_figs(CDF)
          ans=input("S[a]ve plots, <Return> to quit ")
          if ans=="a":
              pmagplotlib.save_plots(CDF,files)
          else:
              sys.exit()
          
      else: 
          pmagplotlib.save_plots(CDF,files)
          sys.exit()