Carpet: Add new parameter Carpet::refine_timestep

Add a new parameter Carpet::refine_timestep which automatically adjusts
the time step size according to the give spatial and temporal refinement
factors, so that the specified CFL factor Time::dtfac is satisfied on all
refinement levels.

5 files changed, 56 insertions, 0 deletions

diff --git a/Carpet/Carpet/param.ccl b/Carpet/Carpet/param.ccl
index ab643e276..b8f2dbe93 100644
--- a/Carpet/Carpet/param.ccl
+++ b/Carpet/Carpet/param.ccl
@@ -132,6 +132,10 @@ STRING time_refinement_factors "Temporal refinement factors over the coarsest le
   "^[[:space:]]*\[[[:space:]]*[[:digit:]]+[[:space:]]*(,[[:space:]]*[[:digit:]]+[[:space:]]*)*\][[:space:]]*$" :: "[ <tfact>, ... ]"
 } ""
 
+BOOLEAN refine_timestep "Correct Time::dtfac for spacings on finer grids"
+{
+} "no"
+
 
 
 CCTK_INT convergence_level "Convergence level"
diff --git a/Carpet/Carpet/schedule.ccl b/Carpet/Carpet/schedule.ccl
index b202a4a82..3c9322b5f 100644
--- a/Carpet/Carpet/schedule.ccl
+++ b/Carpet/Carpet/schedule.ccl
@@ -16,3 +16,17 @@ schedule CarpetParamCheck at PARAMCHECK
 {
   LANG: C
 } "Parameter checking routine"
+
+
+
+# Correct time step for finer levels when there are non-trivial
+# time refinement factors
+
+if (refine_timestep)
+{
+  SCHEDULE CarpetRefineTimeStep AT basegrid AFTER Time_Simple
+  {
+    LANG: C
+    OPTIONS: singlemap
+  } "Correct time step size for spacing on finer grids"
+}
diff --git a/Carpet/Carpet/src/CarpetBasegrid.cc b/Carpet/Carpet/src/CarpetBasegrid.cc
new file mode 100644
index 000000000..c2dc45f81
--- /dev/null
+++ b/Carpet/Carpet/src/CarpetBasegrid.cc
@@ -0,0 +1,36 @@
+#include <limits>
+
+#include "cctk.h"
+#include "cctk_Arguments.h"
+#include "cctk_Parameters.h"
+
+#include "carpet.hh"
+
+
+
+namespace Carpet {
+  
+  using namespace std;
+  
+  void CarpetRefineTimeStep (CCTK_ARGUMENTS)
+  {
+    DECLARE_CCTK_ARGUMENTS;
+    DECLARE_CCTK_PARAMETERS;
+    
+    // Find the smallest CFL factor for all refinement levels
+    CCTK_REAL min_cfl = numeric_limits<CCTK_REAL>::max();
+    for (int rl = 0; rl < reflevels; ++ rl) {
+      CCTK_REAL const level_cfl =
+        timereffacts.AT(rl) / maxval (spacereffacts.AT(rl));
+      min_cfl = min (min_cfl, level_cfl);
+    }
+    
+    // Reduce the time step correspondingly
+    cctkGH->cctk_delta_time *= min_cfl;
+    CCTK_VInfo (CCTK_THORNSTRING,
+                "Timestep reduced by a factor of %g to %g",
+                double (1 / min_cfl),
+                double (cctkGH->cctk_delta_time/cctkGH->cctk_timefac));
+  }
+  
+} // namespace Carpet
diff --git a/Carpet/Carpet/src/carpet.hh b/Carpet/Carpet/src/carpet.hh
index 271a86086..16dca4228 100644
--- a/Carpet/Carpet/src/carpet.hh
+++ b/Carpet/Carpet/src/carpet.hh
@@ -22,6 +22,7 @@ namespace Carpet {
     int CarpetStartup (void);
     int CarpetMultiModelStartup (void);
     void CarpetParamCheck (CCTK_ARGUMENTS);
+    void CarpetRefineTimeStep (CCTK_ARGUMENTS);
   }
   
   // Registered functions
diff --git a/Carpet/Carpet/src/make.code.defn b/Carpet/Carpet/src/make.code.defn
index 374e3dad4..1f70291cd 100644
--- a/Carpet/Carpet/src/make.code.defn
+++ b/Carpet/Carpet/src/make.code.defn
@@ -3,6 +3,7 @@
 # Source files in this directory
 SRCS =	AllGatherString.cc			\
 	CallFunction.cc				\
+	CarpetBasegrid.cc			\
 	CarpetParamCheck.cc			\
 	CarpetStartup.cc			\
 	Checksum.cc				\