more docstrings

Author: Michael Zingale

advection/evolve.py

@@ -1,7 +1,19 @@
 from advectiveFluxes import *
 
 def evolve(my_data, dt):
-    """ evolve the advection equations through one timestep """
+    """ 
+    Evolve the linear advection equation through one timestep.  We only
+    consider the "density" variable in the CellCenterData2d object input
+    here.
+
+    Parameters
+    ----------
+    my_data : CellCenterData2d object
+        The data object containing the scalar quantity we are advecting
+    dt : float
+        The timestep to evolve through
+
+    """
 
     dtdx = dt/my_data.grid.dx
     dtdy = dt/my_data.grid.dy

advection/timestep.py

@@ -1,17 +1,10 @@
-"""
-The timestep module computes the advective timestep (CFL) constraint.
-The CFL constraint says that information cannot propagate further than
-one zone per timestep.
-
-We use the driver.cfl parameter to control what fraction of the CFL
-step we actually take.
-"""
-
 SMALL = 1.e-12
 
 def timestep(my_data):
-    """ 
-    compute the CFL timestep for the current patch.
+    """
+    Computes the advective timestep (CFL) constraint.  We use the 
+    driver.cfl parameter to control what fraction of the CFL
+    step we actually take.
     """
 
     rp = my_data.rp