From: Guido van Rossum <guido@python.org>
Date: Mon, 6 Apr 1998 14:12:13 +0000 (+0000)
Subject: Correction to vonmisesvariate() by Magnus Kessler: it should take and
X-Git-Tag: v1.5.1~173
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=5810297052003f28788f6790ac799fe8e5373494;p=thirdparty%2FPython%2Fcpython.git

Correction to vonmisesvariate() by Magnus Kessler: it should take and
return something between 0 and 2*pi.  Also added a reference to the
literature.
---

diff --git a/Lib/random.py b/Lib/random.py
index 49921cb8b343..221bef6d9cfa 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -79,10 +79,17 @@ TWOPI = 2.0*pi
 verify('TWOPI', 6.28318530718)
 
 def vonmisesvariate(mu, kappa):
-	# mu:    mean angle (in radians between 0 and 180 degrees)
+	# mu:    mean angle (in radians between 0 and 2*pi)
 	# kappa: concentration parameter kappa (>= 0)
-	
 	# if kappa = 0 generate uniform random angle
+
+	# Based upon an algorithm published in: Fisher, N.I.,
+	# "Statistical Analysis of Circular Data", Cambridge
+	# University Press, 1993.
+
+	# Thanks to Magnus Kessler for a correction to the
+	# implementation of step 4.
+
 	if kappa <= 1e-6:
 		return TWOPI * random()
 
@@ -104,11 +111,11 @@ def vonmisesvariate(mu, kappa):
 
 	u3 = random()
 	if u3 > 0.5:
-		theta = mu + 0.5*acos(f)
+		theta = (mu % TWOPI) + acos(f)
 	else:
-		theta = mu - 0.5*acos(f)
+		theta = (mu % TWOPI) - acos(f)
 
-	return theta % pi
+	return theta
 
 # -------------------- gamma distribution --------------------