Source code for gpflow.likelihoods.scalar_continuous

# Copyright 2017-2020 The GPflow Contributors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
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# Unless required by applicable law or agreed to in writing, software
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from math import sqrt
from typing import Any, Callable, Optional

import numpy as np
import tensorflow as tf
from check_shapes import check_shapes, inherit_check_shapes

from .. import logdensities
from ..base import MeanAndVariance, TensorType
from ..config import default_likelihood_positive_minimum
from ..utilities.parameter_or_function import (
    ConstantOrFunction,
    ParameterOrFunction,
    evaluate_parameter_or_function,
    prepare_parameter_or_function,
)
from .base import ScalarLikelihood
from .utils import inv_probit


def _lower_bound(value: Optional[float] = None) -> float:
    if value is None:
        return default_likelihood_positive_minimum()
    return value


[docs] class Gaussian(ScalarLikelihood): r""" The Gaussian likelihood is appropriate where uncertainties associated with the data are believed to follow a normal distribution, with constant variance. Very small uncertainties can lead to numerical instability during the optimization process. A lower bound of 1e-6 is therefore imposed on the likelihood variance by default. """ def __init__( self, variance: Optional[ConstantOrFunction] = None, *, scale: Optional[ConstantOrFunction] = None, variance_lower_bound: Optional[float] = None, **kwargs: Any, ) -> None: """ :param variance: The noise variance; must be greater than ``variance_lower_bound``. This is mutually exclusive with `scale`. :param scale: The noise scale; must be greater than ``sqrt(variance_lower_bound)``. This is mutually exclusive with `variance`. :param variance_lower_bound: The lower (exclusive) bound of ``variance``. :param kwargs: Keyword arguments forwarded to :class:`ScalarLikelihood`. """ super().__init__(**kwargs) self.variance_lower_bound = _lower_bound(variance_lower_bound) self.scale_lower_bound = sqrt(self.variance_lower_bound) if scale is None: if variance is None: variance = 1.0 self.variance: Optional[ParameterOrFunction] = prepare_parameter_or_function( variance, lower_bound=self.variance_lower_bound ) self.scale: Optional[ParameterOrFunction] = None else: if variance is None: self.variance = None self.scale = prepare_parameter_or_function( scale, lower_bound=self.scale_lower_bound ) else: assert False, "Cannot set both `variance` and `scale`." @check_shapes( "X: [batch..., N, D]", "return: [broadcast batch..., broadcast N, broadcast P]", ) def _variance(self, X: TensorType) -> tf.Tensor: if self.variance is not None: return evaluate_parameter_or_function( self.variance, X, lower_bound=self.variance_lower_bound ) else: assert self.scale is not None # For mypy. return ( evaluate_parameter_or_function(self.scale, X, lower_bound=self.scale_lower_bound) ** 2 ) @check_shapes( "X: [batch..., N, D]", "return: [batch..., N, 1]", ) def variance_at(self, X: TensorType) -> tf.Tensor: variance = self._variance(X) shape = tf.concat([tf.shape(X)[:-1], [1]], 0) return tf.broadcast_to(variance, shape) @inherit_check_shapes def _scalar_log_prob(self, X: TensorType, F: TensorType, Y: TensorType) -> tf.Tensor: return logdensities.gaussian(Y, F, self._variance(X)) @inherit_check_shapes def _conditional_mean(self, X: TensorType, F: TensorType) -> tf.Tensor: # pylint: disable=R0201 return tf.identity(F) @inherit_check_shapes def _conditional_variance(self, X: TensorType, F: TensorType) -> tf.Tensor: shape = tf.shape(F) return tf.broadcast_to(self._variance(X), shape) @inherit_check_shapes def _predict_mean_and_var( self, X: TensorType, Fmu: TensorType, Fvar: TensorType ) -> MeanAndVariance: return tf.identity(Fmu), Fvar + self._variance(X) @inherit_check_shapes def _predict_log_density( self, X: TensorType, Fmu: TensorType, Fvar: TensorType, Y: TensorType ) -> tf.Tensor: return tf.reduce_sum(logdensities.gaussian(Y, Fmu, Fvar + self._variance(X)), axis=-1) @inherit_check_shapes def _variational_expectations( self, X: TensorType, Fmu: TensorType, Fvar: TensorType, Y: TensorType ) -> tf.Tensor: variance = self._variance(X) return tf.reduce_sum( -0.5 * np.log(2 * np.pi) - 0.5 * tf.math.log(variance) - 0.5 * ((Y - Fmu) ** 2 + Fvar) / variance, axis=-1, )
[docs] class Exponential(ScalarLikelihood): def __init__(self, invlink: Callable[[tf.Tensor], tf.Tensor] = tf.exp, **kwargs: Any) -> None: super().__init__(**kwargs) self.invlink = invlink @inherit_check_shapes def _scalar_log_prob(self, X: TensorType, F: TensorType, Y: TensorType) -> tf.Tensor: return logdensities.exponential(Y, self.invlink(F)) @inherit_check_shapes def _conditional_mean(self, X: TensorType, F: TensorType) -> tf.Tensor: return self.invlink(F) @inherit_check_shapes def _conditional_variance(self, X: TensorType, F: TensorType) -> tf.Tensor: return tf.square(self.invlink(F)) @inherit_check_shapes def _variational_expectations( self, X: TensorType, Fmu: TensorType, Fvar: TensorType, Y: TensorType ) -> tf.Tensor: if self.invlink is tf.exp: return tf.reduce_sum(-tf.exp(-Fmu + Fvar / 2) * Y - Fmu, axis=-1) return super()._variational_expectations(X, Fmu, Fvar, Y)
[docs] class StudentT(ScalarLikelihood): def __init__( self, scale: ConstantOrFunction = 1.0, df: float = 3.0, scale_lower_bound: Optional[float] = None, **kwargs: Any, ) -> None: """ :param scale float: scale parameter :param df float: degrees of freedom """ super().__init__(**kwargs) self.df = df self.scale_lower_bound = _lower_bound(scale_lower_bound) self.scale = prepare_parameter_or_function(scale, lower_bound=self.scale_lower_bound) @check_shapes( "X: [batch..., N, D]", "return: [broadcast batch..., broadcast N, broadcast P]", ) def _scale(self, X: TensorType) -> tf.Tensor: return evaluate_parameter_or_function(self.scale, X, lower_bound=self.scale_lower_bound) @inherit_check_shapes def _scalar_log_prob(self, X: TensorType, F: TensorType, Y: TensorType) -> tf.Tensor: return logdensities.student_t(Y, F, self._scale(X), self.df) @inherit_check_shapes def _conditional_mean(self, X: TensorType, F: TensorType) -> tf.Tensor: return F @inherit_check_shapes def _conditional_variance(self, X: TensorType, F: TensorType) -> tf.Tensor: shape = tf.shape(F) var = (self._scale(X) ** 2) * (self.df / (self.df - 2.0)) return tf.broadcast_to(var, shape)
[docs] class Gamma(ScalarLikelihood): """ Use the transformed GP to give the *scale* (inverse rate) of the Gamma """ def __init__( self, invlink: Callable[[tf.Tensor], tf.Tensor] = tf.exp, shape: ConstantOrFunction = 1.0, shape_lower_bound: Optional[float] = None, **kwargs: Any, ) -> None: super().__init__(**kwargs) self.invlink = invlink self.shape_lower_bound = _lower_bound(shape_lower_bound) self.shape = prepare_parameter_or_function(shape, lower_bound=self.shape_lower_bound) @check_shapes( "X: [batch..., N, D]", "return: [broadcast batch..., broadcast N, broadcast P]", ) def _shape(self, X: TensorType) -> tf.Tensor: return evaluate_parameter_or_function(self.shape, X, lower_bound=self.shape_lower_bound) @inherit_check_shapes def _scalar_log_prob(self, X: TensorType, F: TensorType, Y: TensorType) -> tf.Tensor: return logdensities.gamma(Y, self._shape(X), self.invlink(F)) @inherit_check_shapes def _conditional_mean(self, X: TensorType, F: TensorType) -> tf.Tensor: return self._shape(X) * self.invlink(F) @inherit_check_shapes def _conditional_variance(self, X: TensorType, F: TensorType) -> tf.Tensor: scale = self.invlink(F) return self._shape(X) * (scale ** 2) @inherit_check_shapes def _variational_expectations( self, X: TensorType, Fmu: TensorType, Fvar: TensorType, Y: TensorType ) -> tf.Tensor: if self.invlink is tf.exp: shape = self._shape(X) return tf.reduce_sum( -shape * Fmu - tf.math.lgamma(shape) + (shape - 1.0) * tf.math.log(Y) - Y * tf.exp(-Fmu + Fvar / 2.0), axis=-1, ) else: return super()._variational_expectations(X, Fmu, Fvar, Y)
[docs] class Beta(ScalarLikelihood): """ This uses a reparameterisation of the Beta density. We have the mean of the Beta distribution given by the transformed process: m = invlink(f) and a scale parameter. The familiar α, β parameters are given by m = α / (α + β) scale = α + β so: α = scale * m β = scale * (1-m) """ def __init__( self, invlink: Callable[[tf.Tensor], tf.Tensor] = inv_probit, scale: ConstantOrFunction = 1.0, scale_lower_bound: Optional[float] = None, **kwargs: Any, ) -> None: super().__init__(**kwargs) self.scale_lower_bound = _lower_bound(scale_lower_bound) self.scale = prepare_parameter_or_function(scale, lower_bound=self.scale_lower_bound) self.invlink = invlink @check_shapes( "X: [batch..., N, D]", "return: [broadcast batch..., broadcast N, broadcast P]", ) def _scale(self, X: TensorType) -> tf.Tensor: return evaluate_parameter_or_function(self.scale, X, lower_bound=self.scale_lower_bound) @inherit_check_shapes def _scalar_log_prob(self, X: TensorType, F: TensorType, Y: TensorType) -> tf.Tensor: mean = self.invlink(F) scale = self._scale(X) alpha = mean * scale beta = scale - alpha return logdensities.beta(Y, alpha, beta) @inherit_check_shapes def _conditional_mean(self, X: TensorType, F: TensorType) -> tf.Tensor: return self.invlink(F) @inherit_check_shapes def _conditional_variance(self, X: TensorType, F: TensorType) -> tf.Tensor: mean = self.invlink(F) var = (mean - tf.square(mean)) / (self._scale(X) + 1.0) shape = tf.shape(F) return tf.broadcast_to(var, shape)