MoL: add Multirate capabilities. This add three new multirate RK schemes to MoL.

Flags indicate whether it is time to execute slow RHS computation.
For instance, in the RK4-RK2 scheme, there are 4 substeps in total, but the RK2 RHS are only evaluated in the very first and in the very last step of the four substeps.

From: Christian Reisswig, minor changes by Roland Haas



git-svn-id: http://svn.cactuscode.org/arrangements/CactusNumerical/MoL/trunk@175 578cdeb0-5ea1-4b81-8215-5a3b8777ee0b

1 files changed, 57 insertions, 0 deletions

diff --git a/src/SetTime.c b/src/SetTime.c
index c04cc0b..32e893c 100644
--- a/src/SetTime.c
+++ b/src/SetTime.c
@@ -298,6 +298,63 @@ void MoL_ResetTime(CCTK_ARGUMENTS)
          + ((alpha_array87[substep] - 1)
             * (* Original_Delta_Time) / cctkGH->cctk_timefac));
   }
+  else if (CCTK_EQUALS(ODE_Method,"RK2-MR-2:1"))
+  {
+    const int substep = MoL_Intermediate_Steps - (* MoL_Intermediate_Step);
+
+    CCTK_REAL dt = (*Original_Delta_Time)/cctkGH->cctk_timefac;
+    switch (substep)
+    {
+      case 1:
+      case 2:
+        dt *= 0.5;
+        break;
+      default:
+        dt = 0;
+    }
+    cctkGH->cctk_time = (*Original_Time) - dt;
+  }
+  else if (CCTK_EQUALS(ODE_Method,"RK4-MR-2:1"))
+  {
+    const int substep = MoL_Intermediate_Steps - (* MoL_Intermediate_Step);
+
+    CCTK_REAL dt = (*Original_Delta_Time)/cctkGH->cctk_timefac;
+    switch (substep)
+    {
+      case 1:
+      case 2:
+        dt *= 3.0/4.0;
+        break;
+      case 3:
+      case 4:
+      case 5:
+        dt *= 1.0/2.0;
+        break;
+      case 6:
+      case 7:
+        dt *= 1.0/4.0;
+        break;
+      default:
+        dt = 0;
+    }
+    cctkGH->cctk_time = (*Original_Time) - dt;
+  }
+  else if (CCTK_EQUALS(ODE_Method,"RK4-RK2"))
+  {
+    const int substep = MoL_Intermediate_Steps - (* MoL_Intermediate_Step);
+
+    CCTK_REAL dt = (*Original_Delta_Time)/cctkGH->cctk_timefac;
+    switch (substep)
+    {
+      case 1:
+      case 2:
+        dt *= 0.5;
+        break;
+      default:
+        dt = 0;
+    }
+    cctkGH->cctk_time = (*Original_Time) - dt;
+  }
 #ifdef MOLDEBUG
   printf("MoL has once more reset t (%d): %f.\n", 
          *MoL_Intermediate_Step, cctkGH->cctk_time);