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 49921cb..221bef6 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -79,10 +79,17 @@
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 @@
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 --------------------