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authorRaymond Hettinger <python@rcn.com>2009-02-19 09:50:24 (GMT)
committerRaymond Hettinger <python@rcn.com>2009-02-19 09:50:24 (GMT)
commit8f9a1eee0d99710801117dc313f5588c2a6c22b1 (patch)
treef6471537f411fb30bb8d17df8de4acfe9af24698 /Lib
parente7cb1ce8959a19ef7d07a035cc5bfe0c976fbdbf (diff)
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Inline coefficients in gamma(). Add reflection formula. Add comments.
Diffstat (limited to 'Lib')
-rw-r--r--Lib/test/test_random.py28
1 files changed, 18 insertions, 10 deletions
diff --git a/Lib/test/test_random.py b/Lib/test/test_random.py
index d82d391..8e4639e 100644
--- a/Lib/test/test_random.py
+++ b/Lib/test/test_random.py
@@ -5,7 +5,7 @@ import random
import time
import pickle
import warnings
-from math import log, exp, sqrt, pi, fsum as msum
+from math import log, exp, sqrt, pi, fsum, sin
from test import test_support
class TestBasicOps(unittest.TestCase):
@@ -459,15 +459,23 @@ class MersenneTwister_TestBasicOps(TestBasicOps):
self.assert_(stop < x <= start)
self.assertEqual((x+stop)%step, 0)
-_gammacoeff = (0.9999999999995183, 676.5203681218835, -1259.139216722289,
- 771.3234287757674, -176.6150291498386, 12.50734324009056,
- -0.1385710331296526, 0.9934937113930748e-05, 0.1659470187408462e-06)
-
-def gamma(z, cof=_gammacoeff, g=7):
- z -= 1.0
- s = msum([cof[0]] + [cof[i] / (z+i) for i in range(1,len(cof))])
- z += 0.5
- return (z+g)**z / exp(z+g) * sqrt(2.0*pi) * s
+def gamma(z, sqrt2pi=(2.0*pi)**0.5):
+ # Reflection to right half of complex plane
+ if z < 0.5:
+ return pi / sin(pi*z) / gamma(1.0-z)
+ # Lanczos approximation with g=7
+ az = z + (7.0 - 0.5)
+ return az ** (z-0.5) / exp(az) * sqrt2pi * fsum([
+ 0.9999999999995183,
+ 676.5203681218835 / z,
+ -1259.139216722289 / (z+1.0),
+ 771.3234287757674 / (z+2.0),
+ -176.6150291498386 / (z+3.0),
+ 12.50734324009056 / (z+4.0),
+ -0.1385710331296526 / (z+5.0),
+ 0.9934937113930748e-05 / (z+6.0),
+ 0.1659470187408462e-06 / (z+7.0),
+ ])
class TestDistributions(unittest.TestCase):
def test_zeroinputs(self):