From aecbba2bcfeb44a5cc89fe5d50666792538948b8 Mon Sep 17 00:00:00 2001
From: Valentin Gehrke <madmaurice@zom.bi>
Date: Sat, 23 May 2015 23:44:26 +0200
Subject: [PATCH] Verfahren von Heun

---
 heun.py | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 heun.py

diff --git a/heun.py b/heun.py
new file mode 100644
index 0000000..262dd60
--- /dev/null
+++ b/heun.py
@@ -0,0 +1,22 @@
+# Verfahren von Heun zur numerischen Lösung von Anfangswertaufgaben.
+
+def heun(xk,yk,h,ys):
+    xk1 = xk + h
+    yk1p = yk + h * ys(xk,yk)
+    yk1 = 0.5*(yk+yk1p+h*ys(xk1,yk1p))
+    return (xk1,yk1p)
+
+def run_heun(K,h,x0,y0,ys):
+    if not isinstance(ys,list): ys = [ys]
+    if not isinstance(y0,list): y0 = [y0]
+    xk = x0
+    yk = y0
+    xks = x0
+    yks = [ [v] for v in y0 ]
+
+    for i in range(K):
+        for j in range(len(ys)):
+            xk,yk[j] = heun(xk,yk[j],h,ys[i])
+            xks.append(xk)
+            yks[j].append(yk[j])
+