dx4, dy4, dx2dy2, D = elasprep(dx,dy,Te,E=1E11,nu=0.25)
    
    Defines the variables that are required to create the 2D finite 
    difference solution coefficient matrix

def elasprep(self):
    """
    dx4, dy4, dx2dy2, D = elasprep(dx,dy,Te,E=1E11,nu=0.25)
    
    Defines the variables that are required to create the 2D finite 
    difference solution coefficient matrix
    """
    
    if self.Method != 'SAS_NG':
      self.dx4 = self.dx**4
      self.dy4 = self.dy**4
      self.dx2dy2 = self.dx**2 * self.dy**2
    self.D = self.E*self.Te**3/(12*(1-self.nu**2))