From a4da5ed146ce656d4cacccc24c1cbb3064cd305f Mon Sep 17 00:00:00 2001
From: Craig Warren <craig_warren@me.com>
Date: Fri, 5 May 2023 10:36:04 +0100
Subject: [PATCH] Tweaks to inherit any time step mods from main grid to
 subgrid

---
 gprMax/cmds_singleuse.py        | 2 +-
 gprMax/grid.py                  | 5 +----
 gprMax/subgrids/subgrid_hsg.py  | 2 +-
 gprMax/subgrids/user_objects.py | 6 +++++-
 4 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/gprMax/cmds_singleuse.py b/gprMax/cmds_singleuse.py
index ae451973..ed722d37 100644
--- a/gprMax/cmds_singleuse.py
+++ b/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')
 
diff --git a/gprMax/grid.py b/gprMax/grid.py
index 069a8de2..a4960727 100644
--- a/gprMax/grid.py
+++ b/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."""
diff --git a/gprMax/subgrids/subgrid_hsg.py b/gprMax/subgrids/subgrid_hsg.py
index 007d9177..60e04db7 100644
--- a/gprMax/subgrids/subgrid_hsg.py
+++ b/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')
\ No newline at end of file
+        logger.info(f'[{self.name}] Time step: {self.dt:g} secs')
\ No newline at end of file
diff --git a/gprMax/subgrids/user_objects.py b/gprMax/subgrids/user_objects.py
index d4e12dbd..ef6b38e1 100644
--- a/gprMax/subgrids/user_objects.py
+++ b/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)