Source code for gluonts.distribution.gamma

# Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
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# Licensed under the Apache License, Version 2.0 (the "License").
# You may not use this file except in compliance with the License.
# A copy of the License is located at
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#     http://www.apache.org/licenses/LICENSE-2.0
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# or in the "license" file accompanying this file. This file is distributed
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# Standard library imports
import math
from functools import partial
from typing import Dict, Optional, Tuple, List

# Third-party imports
import numpy as np

# First-party imports
from gluonts.model.common import Tensor
from gluonts.support.util import erf, erfinv
from gluonts.core.component import validated

# Relative imports
from .distribution import Distribution, _sample_multiple, getF, softplus
from .distribution_output import DistributionOutput


[docs]class Gamma(Distribution): r""" Gamma distribution. Parameters ---------- alpha Tensor containing the shape parameters, of shape `(*batch_shape, *event_shape)`. beta Tensor containing the rate parameters, of shape `(*batch_shape, *event_shape)`. F """ is_reparameterizable = False @validated() def __init__(self, alpha: Tensor, beta: Tensor, F=None) -> None: self.alpha = alpha self.beta = beta self.F = ( F if F else getF(alpha) ) # assuming alpha and beta of same type @property def batch_shape(self) -> Tuple: return self.alpha.shape @property def event_shape(self) -> Tuple: return () @property def event_dim(self) -> int: return 0
[docs] def log_prob(self, x: Tensor) -> Tensor: F = self.F alpha, beta = self.alpha, self.beta return ( alpha * F.log(beta) - F.gammaln(alpha) + (alpha - 1) * F.log(x) - beta * x )
@property def mean(self) -> Tensor: return self.alpha / self.beta @property def stddev(self) -> Tensor: return self.F.sqrt(self.alpha) / self.beta
[docs] def sample( self, num_samples: Optional[int] = None, dtype=np.float32 ) -> Tensor: epsilon = np.finfo(dtype).eps # machine epsilon samples = _sample_multiple( partial(self.F.sample_gamma, dtype=dtype), alpha=self.alpha, beta=1.0 / self.beta, num_samples=num_samples, ) return self.F.clip( data=samples, a_min=epsilon, a_max=np.finfo(dtype).max )
@property def args(self) -> List: return [self.alpha, self.beta]
[docs]class GammaOutput(DistributionOutput): args_dim: Dict[str, int] = {"alpha": 1, "beta": 1} distr_cls: type = Gamma
[docs] @classmethod def domain_map(cls, F, alpha, beta): r""" Maps raw tensors to valid arguments for constructing a Gamma distribution. Parameters ---------- F alpha Tensor of shape `(*batch_shape, 1)` beta Tensor of shape `(*batch_shape, 1)` Returns ------- Tuple[Tensor, Tensor] Two squeezed tensors, of shape `(*batch_shape)`: both have entries mapped to the positive orthant. """ epsilon = np.finfo(cls._dtype).eps # machine epsilon alpha = softplus(F, alpha) + epsilon beta = softplus(F, beta) + epsilon return alpha.squeeze(axis=-1), beta.squeeze(axis=-1)
@property def event_shape(self) -> Tuple: return () @property def value_in_support(self) -> float: return 0.5