44 lines
1.7 KiB
Python
44 lines
1.7 KiB
Python
# Copyright 2021 The JAX Authors.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# https://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License
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import scipy.stats as osp_stats
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from jax import lax
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import jax.numpy as jnp
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from jax._src.lax.lax import _const as _lax_const
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from jax._src.numpy.util import _wraps, promote_args_inexact
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from jax._src.scipy.special import gammaln, xlogy
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from jax._src.typing import Array, ArrayLike
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@_wraps(osp_stats.nbinom.logpmf, update_doc=False)
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def logpmf(k: ArrayLike, n: ArrayLike, p: ArrayLike, loc: ArrayLike = 0) -> Array:
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"""JAX implementation of scipy.stats.nbinom.logpmf."""
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k, n, p, loc = promote_args_inexact("nbinom.logpmf", k, n, p, loc)
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one = _lax_const(k, 1)
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y = lax.sub(k, loc)
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comb_term = lax.sub(
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lax.sub(gammaln(lax.add(y, n)), gammaln(n)), gammaln(lax.add(y, one))
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)
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log_linear_term = lax.add(xlogy(n, p), xlogy(y, lax.sub(one, p)))
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log_probs = lax.add(comb_term, log_linear_term)
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return jnp.where(lax.lt(k, loc), -jnp.inf, log_probs)
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@_wraps(osp_stats.nbinom.pmf, update_doc=False)
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def pmf(k: ArrayLike, n: ArrayLike, p: ArrayLike, loc: ArrayLike = 0) -> Array:
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"""JAX implementation of scipy.stats.nbinom.pmf."""
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return lax.exp(logpmf(k, n, p, loc))
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