From 86957ab86e822262cce3bcb81f6c3e3cbaf907e6 Mon Sep 17 00:00:00 2001
From: Anton Khirnov <anton@khirnov.net>
Date: Wed, 11 Jan 2023 15:05:33 +0100
Subject: Add documentation

---
 README    | 23 +++++++++++++++++++++++
 param.ccl |  8 ++++----
 2 files changed, 27 insertions(+), 4 deletions(-)
 create mode 100644 README

diff --git a/README b/README
new file mode 100644
index 0000000..ac30c17
--- /dev/null
+++ b/README
@@ -0,0 +1,23 @@
+This thorn loads stored simulation output to set initial data.
+
+The implementation is very simple - it invokes an external executable (specified
+by the 'load_data_exe' parameter) and reads the values from its stdout. See the
+popen() call in src/revive.c for arguments passed to the binary. The
+implementation this was developed with is [1], but any other executable that
+behaves in a compatible way should work.
+
+Example use:
+ActiveThorns = "ADMBase ReviveData"
+
+ADMBase::initial_data             = "revivedata"
+ADMBase::initial_lapse            = "revivedata"
+ADMBase::initial_dtlapse          = "zero"
+ADMBase::initial_shift            = "revivedata"
+ADMBase::initial_dtshift          = "zero"
+
+ReviveData::load_data_exe = "<...>/revive.py"
+ReviveData::simdata_path  = "<path to stored simulation data"
+ReviveData::load_time     = 10.0
+
+[1] https://git.khirnov.net/cactus_revive.git/
+
diff --git a/param.ccl b/param.ccl
index 3c65ef4..5e70614 100644
--- a/param.ccl
+++ b/param.ccl
@@ -18,20 +18,20 @@ EXTENDS KEYWORD initial_shift
 RESTRICTED:
 STRING load_data_exe ""
 {
-    "" :: ""
+    "" :: "Path to the binary that will provide that data"
 } ""
 
 STRING simdata_path ""
 {
-    "" :: ""
+    "" :: "Path to stored simulation data"
 } ""
 
 REAL load_time ""
 {
-    : :: ""
+    : :: "Simulation time at which to restore the data"
 } 0.0
 
 INT load_iteration ""
 {
-    : :: ""
+    : :: "Simulation iteration at which to restore the data"
 } -1
-- 
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