new_contents: import math
  import numpy
  import pylab
  
  def plot_convergence():
  
      data = numpy.loadtxt("advection_convergence.txt")
  
      nx = data[:,0]
      aerr_lim1 = data[:,1]
      aerr_lim2 = data[:,3]
  
      ax = pylab.subplot(111)
      ax.set_xscale('log')
      ax.set_yscale('log')
  
      pylab.scatter(nx, aerr_lim2, marker="x", color="r")
      pylab.plot(nx, aerr_lim2[0]*(nx[0]/nx)**2, "--", color="k")
  
      pylab.xlabel("number of zones")
      pylab.ylabel("L2 norm of abs error")
  
      pylab.title(r"convergence for smooth advection problem", fontsize=11)
  
      f = pylab.gcf()
      f.set_size_inches(5.0,5.0)
  
      pylab.xlim(8,256)
  
      pylab.savefig("smooth_converge.png", bbox_inches="tight")
  
      
  
  if __name__== "__main__":
      plot_convergence()
  
  
subject: add convergence plot