code: def _get_qtyprc(self, n_points=6):
          
          if self.pcost_model == POLYNOMIAL:
              # Convert polynomial cost function to piece-wise linear.
              self.poly_to_pwl(n_points)
  
          n_segments = len(self.p_cost) - 1
  
          qtyprc = []
  
          for i in range(n_segments):
              x1, y1 = self.p_cost[i]
              x2, y2 = self.p_cost[(i + 1)]
  
              quantity = x2 - x1
              price = (y2 - y1) / quantity
  
              qtyprc.append((quantity, price))
  
          return qtyprc
docs: Returns a list of tuples of the form (qty, prc) created from the
          cost function.  If the cost function is polynomial it will be converted
          to piece-wise linear using poly_to_pwl(n_points).