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| author | Warren Weckesser <warren.weckesser@gmail.com> | 2020-04-05 23:25:53 -0400 |
|---|---|---|
| committer | Warren Weckesser <warren.weckesser@gmail.com> | 2020-04-05 23:35:50 -0400 |
| commit | f90f26c40ac4b37e1df8c76ee6745433557d999b (patch) | |
| tree | 57af5f657f9769fdab28eb1dd45dd621c14fa7fe /numpy/random | |
| parent | 0f6a3aaa34fe72586f8c66ecc4744fc960d62ae2 (diff) | |
| download | numpy-f90f26c40ac4b37e1df8c76ee6745433557d999b.tar.gz | |
BUG: random: Disallow p=0 in negative_binomial
Make `Generator.negative_binomial` raise a ValueError if p=0.
`negative_binomial(n, p)` draws samples from the distribution of
the number of failures until n successes are encountered. If p is 0,
then a success is never encountered, so the probability distribution
is 0 for any finite number of failures. In other words, it is not
really a meaningful distribution, so we disallow p=0.
Closes gh-15913.
Diffstat (limited to 'numpy/random')
| -rw-r--r-- | numpy/random/_generator.pyx | 6 | ||||
| -rw-r--r-- | numpy/random/tests/test_generator_mt19937.py | 5 |
2 files changed, 8 insertions, 3 deletions
diff --git a/numpy/random/_generator.pyx b/numpy/random/_generator.pyx index 6b8a2f70b..27e006cc3 100644 --- a/numpy/random/_generator.pyx +++ b/numpy/random/_generator.pyx @@ -2844,14 +2844,14 @@ cdef class Generator: Samples are drawn from a negative binomial distribution with specified parameters, `n` successes and `p` probability of success where `n` - is > 0 and `p` is in the interval [0, 1]. + is > 0 and `p` is in the interval (0, 1]. Parameters ---------- n : float or array_like of floats Parameter of the distribution, > 0. p : float or array_like of floats - Parameter of the distribution, >= 0 and <=1. + Parameter of the distribution. Must satisfy 0 < p <= 1. size : int or tuple of ints, optional Output shape. If the given shape is, e.g., ``(m, n, k)``, then ``m * n * k`` samples are drawn. If size is ``None`` (default), @@ -2909,7 +2909,7 @@ cdef class Generator: """ return disc(&random_negative_binomial, &self._bitgen, size, self.lock, 2, 0, n, 'n', CONS_POSITIVE_NOT_NAN, - p, 'p', CONS_BOUNDED_0_1, + p, 'p', CONS_BOUNDED_GT_0_1, 0.0, '', CONS_NONE) def poisson(self, lam=1.0, size=None): diff --git a/numpy/random/tests/test_generator_mt19937.py b/numpy/random/tests/test_generator_mt19937.py index b10c1310e..c4c1fa316 100644 --- a/numpy/random/tests/test_generator_mt19937.py +++ b/numpy/random/tests/test_generator_mt19937.py @@ -1297,6 +1297,11 @@ class TestRandomDist: assert_raises(ValueError, random.negative_binomial, 100, [np.nan] * 10) + def test_negative_binomial_p0_exception(self): + # Verify that p=0 raises an exception. + with assert_raises(ValueError): + x = random.negative_binomial(1, 0) + def test_noncentral_chisquare(self): random = Generator(MT19937(self.seed)) actual = random.noncentral_chisquare(df=5, nonc=5, size=(3, 2)) |