From ebcceefe4c86ccd91880f6795ddce1755d199aab Mon Sep 17 00:00:00 2001
From: Henri Saudubray <henri.saudubray@proton.me>
Date: Tue, 29 Apr 2025 16:20:25 +0200
Subject: [PATCH] feat (exm): sqrt example

---
 exm/sqrt.ml     | 79 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/bin/main.ml |  1 +
 2 files changed, 80 insertions(+)
 create mode 100644 exm/sqrt.ml

diff --git a/exm/sqrt.ml b/exm/sqrt.ml
new file mode 100644
index 0000000..19cdb55
--- /dev/null
+++ b/exm/sqrt.ml
@@ -0,0 +1,79 @@
+
+open Hsim.Types
+open Solvers.Zls
+
+let of_array a = Bigarray.Array1.of_array Bigarray.Float64 Bigarray.c_layout a
+
+type s = Good | Bad
+
+let with_nan = false
+
+type state = 
+  { s_auto: s; (* active state of the automaton *)
+    s_pos : carray;
+    s_zin : zarray;
+    s_encore : bool }
+
+let sqrt () =
+  let zfalse = zmake 1 in
+  let fder s y yd =
+    yd.{0} <- -1.0;
+    match s.s_auto with
+    | Good -> 
+        let o = if with_nan then sqrt y.{0}
+                else if y.{0} >= 0.0 then sqrt y.{0} else 0.0 in
+        yd.{1} <- o
+    | Bad ->
+        yd.{1} <- 0.0 in
+  let fzero _ y zout = zout.{0} <- -. y.{0} in
+  let fout state y =
+    let o = 
+      match state.s_auto with
+      | Good -> let o = 
+                  if with_nan then sqrt y.{0}
+                  else if y.{0} >= 0.0 then sqrt y.{0} else 0.0 in
+                o
+      | Bad -> let o = 42.0 in o in
+    of_array [| o; state.s_pos.{0}; state.s_pos.{1} |] in
+  let fstep ({ s_auto; s_pos; s_zin; _ } as state) _ =
+    match s_auto with
+      | Good ->
+         let o = if with_nan then sqrt s_pos.{0}
+                 else if s_pos.{0} >= 0.0 then sqrt s_pos.{0} else 0.0 in
+         let state = 
+           if s_zin.{0} = 1l then { state with s_auto = Bad; s_encore = true } 
+           else state in
+         let pos = of_array [| state.s_pos.{0}; state.s_pos.{1} |] in
+         of_array [| o; state.s_pos.{0}; state.s_pos.{1} |], 
+         { state with s_zin = zfalse; s_pos = pos } 
+    | Bad -> 
+       let o = 42.0 in
+       let state = { state with s_encore = false;
+                                s_pos = 
+                                  of_array [| s_pos.{0}; 0.0 |] } in
+       of_array [| o; state.s_pos.{0}; state.s_pos.{1} |], state in
+  let cget { s_pos; _ } = s_pos in
+  let cset s l_x = { s with s_pos = l_x } in
+  let zset s zin = { s with s_zin = zin } in
+  let yd = cmake 2 in
+  let zout = cmake 1 in
+  let zsize = 1 in
+  let s_init =
+    { s_encore = false;
+      s_auto = Good;
+      s_pos = of_array [| 13.3; 0.0 |]; 
+      s_zin = zmake 1 } in
+  let reset _ _ = s_init in
+  let jump _ = true in
+  HNode { state = s_init;
+    fder = (fun s _ y -> fder s y yd; yd);
+    fzer = (fun s _ y -> fzero s y zout; zout);
+    fout = (fun s _ y -> fout s y);
+    step = (fun s a -> fstep s a);
+    horizon = (fun s -> if s.s_encore then 0.0 else max_float);
+    cset; cget; zset; zsize; reset; jump }
+
+let errmsg = "Too many arguments to model (needed: 0)"
+let sqrt = function
+  | [] -> sqrt ()
+  | _  -> raise (Invalid_argument errmsg)
diff --git a/src/bin/main.ml b/src/bin/main.ml
index 8c8f920..41dbc6a 100644
--- a/src/bin/main.ml
+++ b/src/bin/main.ml
@@ -43,6 +43,7 @@ let m = match !model with
   | "ball"   -> Ball.bouncing_ball
   | "vdp"    -> Vdp.van_der_pol
   | "sincos" -> Sincos.sinus_cosinus
+  | "sqrt"   -> Sqrt.sqrt
   | _        -> eprintf "Unknown model: %s\n" !model; exit 2
 let m = try m !modelargs with Invalid_argument s -> eprintf "%s\n" s; exit 2