Closes patch 529408 deprecating random.stdgamma().
diff --git a/Lib/random.py b/Lib/random.py
index affa381..8747b06 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -445,14 +445,15 @@
## -------------------- gamma distribution --------------------
def gammavariate(self, alpha, beta):
- # beta times standard gamma
- return beta * self.stdgamma(alpha)
-
- def stdgamma(self, alpha, *args): # *args for Py2.2 compatiblity
+
+ # alpha > 0, beta > 0, mean is alpha*beta, variance is alpha*beta**2
+
+ # Warning: a few older sources define the gamma distribution in terms
+ # of alpha > -1.0
+ if alpha <= 0.0 or beta <= 0.0:
+ raise ValueError, 'gammavariate: alpha and beta must be > 0.0'
+
random = self.random
- if alpha <= 0.0:
- raise ValueError, 'stdgamma: alpha must be > 0.0'
-
if alpha > 1.0:
# Uses R.C.H. Cheng, "The generation of Gamma
@@ -471,14 +472,14 @@
z = u1*u1*u2
r = bbb+ccc*v-x
if r + SG_MAGICCONST - 4.5*z >= 0.0 or r >= _log(z):
- return x
+ return x * beta
elif alpha == 1.0:
# expovariate(1)
u = random()
while u <= 1e-7:
u = random()
- return -_log(u)
+ return -_log(u) * beta
else: # alpha is between 0 and 1 (exclusive)
@@ -497,7 +498,27 @@
if not (((p <= 1.0) and (u1 > _exp(-x))) or
((p > 1) and (u1 > pow(x, alpha - 1.0)))):
break
- return x
+ return x * beta
+
+
+ def stdgamma(self, alpha, ainv, bbb, ccc):
+ # This method was (and shall remain) undocumented.
+ # This method is deprecated
+ # for the following reasons:
+ # 1. Returns same as .gammavariate(alpha, 1.0)
+ # 2. Requires caller to provide 3 extra arguments
+ # that are functions of alpha anyway
+ # 3. Can't be used for alpha < 0.5
+
+ # ainv = sqrt(2 * alpha - 1)
+ # bbb = alpha - log(4)
+ # ccc = alpha + ainv
+ import warnings
+ warnings.warn("The stdgamma function is deprecated; "
+ "use gammavariate() instead",
+ DeprecationWarning)
+ return self.gammavariate(alpha, 1.0)
+
## -------------------- Gauss (faster alternative) --------------------
@@ -596,7 +617,7 @@
print 'avg %g, stddev %g, min %g, max %g' % \
(avg, stddev, smallest, largest)
-def _test(N=200):
+def _test(N=20000):
print 'TWOPI =', TWOPI
print 'LOG4 =', LOG4
print 'NV_MAGICCONST =', NV_MAGICCONST
@@ -607,6 +628,9 @@
_test_generator(N, 'cunifvariate(0.0, 1.0)')
_test_generator(N, 'expovariate(1.0)')
_test_generator(N, 'vonmisesvariate(0.0, 1.0)')
+ _test_generator(N, 'gammavariate(0.01, 1.0)')
+ _test_generator(N, 'gammavariate(0.1, 1.0)')
+ _test_generator(N, 'gammavariate(0.1, 2.0)')
_test_generator(N, 'gammavariate(0.5, 1.0)')
_test_generator(N, 'gammavariate(0.9, 1.0)')
_test_generator(N, 'gammavariate(1.0, 1.0)')