Issue 1681432: Add triangular distribution the random module.
diff --git a/Doc/library/random.rst b/Doc/library/random.rst
index 3beed6c..505cc81 100644
--- a/Doc/library/random.rst
+++ b/Doc/library/random.rst
@@ -190,6 +190,10 @@
Return a random floating point number *N* such that ``a <= N < b``.
+.. function:: triangular(low, high, mode)
+
+ Return a random floating point number *N* such that ``low <= N < high``
+ and with the specified *mode* between those bounds.
.. function:: betavariate(alpha, beta)
diff --git a/Lib/random.py b/Lib/random.py
index ec0f386..13125e2 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -13,6 +13,7 @@
distributions on the real line:
------------------------------
uniform
+ triangular
normal (Gaussian)
lognormal
negative exponential
@@ -47,7 +48,7 @@
__all__ = ["Random","seed","random","uniform","randint","choice","sample",
"randrange","shuffle","normalvariate","lognormvariate",
- "expovariate","vonmisesvariate","gammavariate",
+ "expovariate","vonmisesvariate","gammavariate","triangular",
"gauss","betavariate","paretovariate","weibullvariate",
"getstate","setstate","jumpahead", "WichmannHill", "getrandbits",
"SystemRandom"]
@@ -350,6 +351,25 @@
"""Get a random number in the range [a, b)."""
return a + (b-a) * self.random()
+## -------------------- triangular --------------------
+
+ def triangular(self, low, high, mode):
+ """Triangular distribution.
+
+ Continuous distribution bounded by given lower and upper limits,
+ and having a given mode value in-between.
+
+ http://en.wikipedia.org/wiki/Triangular_distribution
+
+ """
+ u = self.random()
+ c = (mode - low) / (high - low)
+ if u > c:
+ u = 1 - u
+ c = 1 - c
+ low, high = high, low
+ return low + (high - low) * (u * c) ** 0.5
+
## -------------------- normal distribution --------------------
def normalvariate(self, mu, sigma):
@@ -839,6 +859,7 @@
_test_generator(N, gammavariate, (200.0, 1.0))
_test_generator(N, gauss, (0.0, 1.0))
_test_generator(N, betavariate, (3.0, 3.0))
+ _test_generator(N, triangular, (0.0, 1.0, 1.0/3.0))
# Create one instance, seeded from current time, and export its methods
# as module-level functions. The functions share state across all uses
@@ -850,6 +871,7 @@
seed = _inst.seed
random = _inst.random
uniform = _inst.uniform
+triangular = _inst.triangular
randint = _inst.randint
choice = _inst.choice
randrange = _inst.randrange
diff --git a/Lib/test/test_random.py b/Lib/test/test_random.py
index 86e2e64..07e12d3 100644
--- a/Lib/test/test_random.py
+++ b/Lib/test/test_random.py
@@ -488,6 +488,7 @@
g.random = x[:].pop; g.gammavariate(1.0, 1.0)
g.random = x[:].pop; g.gammavariate(200.0, 1.0)
g.random = x[:].pop; g.betavariate(3.0, 3.0)
+ g.random = x[:].pop; g.triangular(0.0, 1.0, 1.0/3.0)
def test_avg_std(self):
# Use integration to test distribution average and standard deviation.
@@ -497,6 +498,7 @@
x = [i/float(N) for i in xrange(1,N)]
for variate, args, mu, sigmasqrd in [
(g.uniform, (1.0,10.0), (10.0+1.0)/2, (10.0-1.0)**2/12),
+ (g.triangular, (0.0, 1.0, 1.0/3.0), 4.0/9.0, 7.0/9.0/18.0),
(g.expovariate, (1.5,), 1/1.5, 1/1.5**2),
(g.paretovariate, (5.0,), 5.0/(5.0-1),
5.0/((5.0-1)**2*(5.0-2))),
diff --git a/Misc/NEWS b/Misc/NEWS
index f7b16b4..04dec03 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -66,6 +66,8 @@
- Issue #2432: give DictReader the dialect and line_num attributes
advertised in the docs.
+- Issue #1681432: Add triangular distribution to the random module
+
- Issue #2136: urllib2's auth handler now allows single-quoted realms in the
WWW-Authenticate header.