Fixed bug in calculation of 'cfl_number' in last time step.

DG_Approximation.py

@@ -7,6 +7,7 @@ TODO: Double-check everything!
 TODO: Replace loops with list comprehension if feasible
 TODO: Write documentation for all methods
 TODO: Contemplate how to make shock tubes comparable
+TODO: Fix bug in approximation -> Done (used num_grid_cells instead of cell_len for cfl_number in last step)
 
 """
 import numpy as np
@@ -103,7 +104,7 @@ class DGScheme(object):
             cfl_number = self._cfl_number
             if current_time+time_step > self._final_time:
                 time_step = self._final_time-current_time
-                cfl_number = self._wave_speed * time_step / self._num_grid_cells
+                cfl_number = self._wave_speed * time_step / self._cell_len
 
             # Update projection
             projection, troubled_cells = self._update_scheme.step(projection, cfl_number)