Tweaks to inherit any time step mods from main grid to subgrid

gprMax/cmds_singleuse.py

@@ -191,7 +191,7 @@ class TimeStepStabilityFactor(UserObjectSingle):
             raise ValueError
         
         G.dt_mod = f
-        G.calculate_dt()
+        G.dt = G.dt * G.dt_mod
 
         logger.info(f'Time step (modified): {G.dt:g} secs')
 

gprMax/grid.py

@@ -46,7 +46,7 @@ class FDTDGrid:
         self.dy = 0
         self.dz = 0
         self.dt = 0
-        self.dt_mod = 1 # Time step stability factor
+        self.dt_mod = None # Time step stability factor
         self.iteration = 0 # Current iteration number
         self.iterations = 0 # Total number of iterations
         self.timewindow = 0
@@ -299,9 +299,6 @@ class FDTDGrid:
         # binary representation of floating point number.
         self.dt = round_value(self.dt, decimalplaces=d.getcontext().prec - 1)
 
-        # Apply any time step stability factor
-        self.dt = self.dt * self.dt_mod
-
 
 class CUDAGrid(FDTDGrid):
     """Additional grid methods for solving on GPU using CUDA."""

gprMax/subgrids/subgrid_hsg.py

@@ -294,4 +294,4 @@ class SubGridHSG(SubGridBaseGrid):
                     f'(({self.nwx} x {self.nwy} x {self.nwz} = {self.nwx * self.nwy * self.nwz} cells)')
         logger.debug(f'[{self.name}] Total region: {self.nx:d} x {self.ny:d} x {self.nz:d} = ' +
                      f'{(self.nx * self.ny * self.nz):g} cells')
-        logger.info(f'[{self.name}] Time step (at CFL limit): {self.dt:g} secs')
+        logger.info(f'[{self.name}] Time step: {self.dt:g} secs')

gprMax/subgrids/user_objects.py

@@ -91,8 +91,12 @@ class SubGridBase(UserObjectMulti):
 
         self.set_discretisation(sg, grid)
 
-        # Set temporal discretisation
+        # Set temporal discretisation including any inherited time step 
+        # stability factor from the main grid
         sg.calculate_dt()
+        if grid.dt_mod:
+            sg.dt = sg.dt * grid.dt_mod
+
 
         # Set the indices related to the subgrids main grid placement
         self.set_main_grid_indices(sg, uip, p1, p2)