title: TypeError: unsupported operand type(s) for /: 'float' and 'instancemethod'
body: <p>I am getting the following error when I tried debug this code for other errors. </p>
  
  <pre><code>Traceback (most recent call last):
    File "testSweep.py", line 43, in &lt;module&gt;
      print sweep_operator(mesh, q)
    File "testSweep.py", line 32, in sweep_operator
      a = 2.0 * mu / dx
  TypeError: unsupported operand type(s) for /: 'float' and 'instancemethod'
  </code></pre>
  
  <p>Any suggestion on this?</p>
  
  <pre><code>import numpy as np
  class Mesh():
      def __init__(self, num_cells, num_angles, sigma_t, sigma_s, length):
          self.num_cells = num_cells 
          self.num_angles = num_angles 
          self.sigma_t = sigma_t  
          self.sigma_s = sigma_s 
          self.length = length   
  
      def dx(self, dif):
      # get the width of each cell
          self.dif = self.num_cells/self.length
          return self.dif
  
  def sweep_operator(mesh, q) :
      mu, w = np.polynomial.legendre.leggauss(2*mesh.num_angles)
      mu = mu[mesh.num_angles:]
      w  = w[mesh.num_angles:]
      phi = np.zeros(mesh.num_cells)
  
      for o in range(0, 2) : 
          psi_edge = np.zeros(mesh.num_angles)
          i_min = 0; i_max = mesh.num_cells; i_inc = 1
          if o :
              i_min = mesh.num_cells-1; i_max = -1; i_inc = -1
          for i in range(i_min, i_max, i_inc) :
              a = 2.0 * mu / dx
              b = 1.0 / (mesh.sigma_t + a)
              psi_center = b * (q + a[:] * psi_edge[:]) 
              psi_edge[:] = 2.0*psi_center[:] - psi_edge[:]            
              phi[i] += np.dot(psi_center, w)
      return phi
  
  
  mesh = Mesh(1000, 4, 1.0, 0.5, 10)
  q = 1.0
  dx = mesh.dx
  print sweep_operator(mesh, q)
  </code></pre>