From a69ca9960f5eed7aec267de705a2b8554fe5c450 Mon Sep 17 00:00:00 2001
From: allen <allen@5633253d-7678-4964-a54d-f87795f8ee59>
Date: Tue, 12 Sep 2000 07:45:27 +0000
Subject: Adding fixed timestep option

Will update documentation.tex later today.


git-svn-id: http://svn.cactuscode.org/arrangements/CactusBase/Time/trunk@27 5633253d-7678-4964-a54d-f87795f8ee59
---
 README             | 13 ++++++++++---
 param.ccl          | 29 +++++++++++++++++++----------
 schedule.ccl       | 11 ++++++++---
 src/Given.c        | 25 +++++++++++++++++++++++++
 src/make.code.defn |  2 +-
 5 files changed, 63 insertions(+), 17 deletions(-)
 create mode 100644 src/Given.c

diff --git a/README b/README
index aae1da0..3f731b9 100644
--- a/README
+++ b/README
@@ -3,8 +3,15 @@ Authors    : Gabrielle Allen
 CVS info   : $Header$
 --------------------------------------------------------------------------
 
-Thorn Time sets the timestep for an evolution. Currently it
-uses a simple Courant condition with speed one. That is
+Thorn Time sets the timestep for the simulation by either
+
+	- setting the timestep directly from a parameter value
+
+	- using a Courant-type condition to set the timestep based
+	  on the grid-spacing used.
+
+The Courant condition can be applied either once at the start of the
+simulation, or the timestep can be calculated dynamically before each timestep.
+
 
-cctk_delta_time = dtfac * min(cctk_delta_space)
 
diff --git a/param.ccl b/param.ccl
index 317be03..79ce823 100644
--- a/param.ccl
+++ b/param.ccl
@@ -3,18 +3,9 @@
 
 restricted:
 
-REAL dtfac "The standard timestep condition dt = dtfac*max(delta_space)"
-{
- 0:* :: "Probably only makes sense to be bigger than zero"
-} 0.5 
-
-REAL courant_fac "The courant timestep condition dt = courant_fac*max(delta_space)/speed/sqrt(dim)"
-{
- 0:* :: "Probably only makes sense to be bigger than zero"
-} 0.9
-
 KEYWORD courant_method "Method for calculating timestep"
 {
+ "none"     :: "Use given timestep"
  "standard" :: "Courant condition at BASEGRID"
  "courant"  :: "Courant condition at PRESTEP (using wavespeed)"
  "courant_time" :: "Courant condition at PRESTEP (using min time)"
@@ -24,6 +15,24 @@ BOOLEAN courant_outonly "Only output courant timestep?"
 {
 } "no"
 
+
+private:
+
+REAL timestep "Absolute value for timestep"
+{
+ *:* :: "Could be anything"
+} 0.0
+
+REAL dtfac "The standard timestep condition dt = dtfac*max(delta_space)"
+{
+ 0:* :: "Probably only makes sense to be bigger than zero"
+} 0.5 
+
+REAL courant_fac "The courant timestep condition dt = courant_fac*max(delta_space)/speed/sqrt(dim)"
+{
+ 0:* :: "Probably only makes sense to be bigger than zero"
+} 0.9
+
 INT outcourant_every "How often to output courant timestep"
 {
  0:* :: "Zero means no output"
diff --git a/schedule.ccl b/schedule.ccl
index 84b646f..2399f7f 100644
--- a/schedule.ccl
+++ b/schedule.ccl
@@ -8,8 +8,7 @@ if (CCTK_Equals(courant_method,"standard"))
      LANG: C
   } "Set timestep based on Courant condition"
 }
-
-if (CCTK_Equals(courant_method,"courant") || CCTK_Equals(courant_method,"courant_time"))
+else if (CCTK_Equals(courant_method,"courant") || CCTK_Equals(courant_method,"courant_time"))
 {
   schedule Time_Simple at CCTK_BASEGRID after SpatialCoordinates
   {
@@ -21,6 +20,12 @@ if (CCTK_Equals(courant_method,"courant") || CCTK_Equals(courant_method,"courant
     LANG: C
   } "Reset timestep each iteration"
 }
-  
+else 
+{
+  schedule Time_Given at CCTK_BASEGRID
+  {
+     LANG: C
+  } "Set fixed timestep"
+}  
 
 
diff --git a/src/Given.c b/src/Given.c
new file mode 100644
index 0000000..645c422
--- /dev/null
+++ b/src/Given.c
@@ -0,0 +1,25 @@
+ /*@@
+   @file      Simple.c
+   @date      September 4 1999
+   @author    Gabrielle Allen
+   @desc 
+   Standard specification of timestep
+   @enddesc 
+ @@*/
+
+#include <stdlib.h>
+
+#include "cctk.h"
+#include "cctk_Arguments.h"
+#include "cctk_Parameters.h"
+
+void Time_Given(CCTK_ARGUMENTS)
+{
+  DECLARE_CCTK_PARAMETERS
+  DECLARE_CCTK_ARGUMENTS
+
+  cctkGH->cctk_delta_time = timestep;  
+}
+
+
+
diff --git a/src/make.code.defn b/src/make.code.defn
index a37cea0..4571048 100644
--- a/src/make.code.defn
+++ b/src/make.code.defn
@@ -2,7 +2,7 @@
 # $Header$
 
 # Source files in this directory
-SRCS = Simple.c Courant.c
+SRCS = Simple.c Courant.c Given.c
 
 # Subdirectories containing source files
 SUBDIRS = 
-- 
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