Source code for

# Copyright (c) 2017-2019 Uber Technologies, Inc.
# SPDX-License-Identifier: Apache-2.0

import torch

import pyro
import pyro.distributions as dist
from import Likelihood

[docs]class Poisson(Likelihood): """ Implementation of Poisson likelihood, which is used for count data. Poisson likelihood uses the :class:`~pyro.distributions.Poisson` distribution, so the output of ``response_function`` should be positive. By default, we use :func:`torch.exp` as response function, corresponding to a log-Gaussian Cox process. :param callable response_function: A mapping to positive real numbers. """ def __init__(self, response_function=None): super().__init__() self.response_function = ( torch.exp if response_function is None else response_function )
[docs] def forward(self, f_loc, f_var, y=None): r""" Samples :math:`y` given :math:`f_{loc}`, :math:`f_{var}` according to .. math:: f & \sim \mathbb{Normal}(f_{loc}, f_{var}),\\ y & \sim \mathbb{Poisson}(\exp(f)). .. note:: The log likelihood is estimated using Monte Carlo with 1 sample of :math:`f`. :param torch.Tensor f_loc: Mean of latent function output. :param torch.Tensor f_var: Variance of latent function output. :param torch.Tensor y: Training output tensor. :returns: a tensor sampled from likelihood :rtype: torch.Tensor """ # calculates Monte Carlo estimate for E_q(f) [logp(y | f)] f = dist.Normal(f_loc, f_var.sqrt())() f_res = self.response_function(f) y_dist = dist.Poisson(f_res) if y is not None: y_dist = y_dist.expand_by(y.shape[: -f_res.dim()]).to_event(y.dim()) return pyro.sample(self._pyro_get_fullname("y"), y_dist, obs=y)