Source code for autofit.mapper.prior.log_uniform

from typing import Optional

import numpy as np

from autofit import exc
from autofit.messages.normal import UniformNormalMessage
from autofit.messages.transform import log_10_transform, LinearShiftTransform
from .abstract import Prior
from ...messages.composed_transform import TransformedMessage


class LogUniformPrior(Prior):
    def __init__(
        self,
        lower_limit: float = 1e-6,
        upper_limit: float = 1.0,
        id_: Optional[int] = None,
    ):
        """
        A prior with a log base 10 uniform distribution, defined between a lower limit and upper limit.

        The conversion of an input unit value, ``u``, to a physical value, ``p``, via the prior is as follows:

        .. math::

        For example for ``prior = LogUniformPrior(lower_limit=10.0, upper_limit=1000.0)``, an
        input ``prior.value_for(unit=0.5)`` is equal to 100.0.

        [Rich describe how this is done via message]

        Parameters
        ----------
        lower_limit
            The lower limit of the log10 uniform distribution defining the prior.
        upper_limit
            The upper limit of the log10 uniform distribution defining the prior.

        Examples
        --------

        prior = af.LogUniformPrior(lower_limit=0.0, upper_limit=2.0)

        physical_value = prior.value_for(unit=0.2)
        """

        if lower_limit <= 0.0:
            raise exc.PriorException(
                "The lower limit of a LogUniformPrior cannot be zero or negative."
            )

        lower_limit = float(lower_limit)
        upper_limit = float(upper_limit)

        message = TransformedMessage(
            UniformNormalMessage,
            LinearShiftTransform(
                shift=np.log10(lower_limit),
                scale=np.log10(upper_limit / lower_limit),
            ),
            log_10_transform,
        )

        super().__init__(
            message=message,
            lower_limit=lower_limit,
            upper_limit=upper_limit,
            id_=id_,
        )

    @classmethod
    def with_limits(cls, lower_limit: float, upper_limit: float) -> "LogUniformPrior":
        """
        Create a new log 10 uniform prior centred between two limits
        with sigma distance between this limits.

        Note that these limits are not strict so exceptions will not
        be raised for values outside of the limits.

        This function is typically used in prior passing, where the
        result of a model-fit are used to create new Gaussian priors
        centred on the previously estimated median PDF model.

        Parameters
        ----------
        lower_limit
            The lower limit of the new LogUniform prior.
        upper_limit
            The upper limit of the new LogUniform Prior.

        Returns
        -------
        A new LogUniform.
        """
        return cls(
            lower_limit=max(0.000001, lower_limit),
            upper_limit=upper_limit,
        )

    __identifier_fields__ = ("lower_limit", "upper_limit")

    def log_prior_from_value(self, value) -> float:
        """
        Returns the log prior of a physical value, so the log likelihood of a model evaluation can be converted to a
        posterior as log_prior + log_likelihood.

        This is used by certain non-linear searches (e.g. Emcee) in the log likelihood function evaluation.

        Parameters
        ----------
        value : float
            The physical value of this prior's corresponding parameter in a `NonLinearSearch` sample.
        """
        return 1.0 / value

    def value_for(self, unit: float, ignore_prior_limits: bool = False) -> float:
        """
        Returns a physical value from an input unit value according to the limits of the log10 uniform prior.

        Parameters
        ----------
        unit
            A unit value between 0 and 1.

        Returns
        -------
        value
            The unit value mapped to a physical value according to the prior.

        Examples
        --------

        prior = af.LogUniformPrior(lower_limit=0.0, upper_limit=2.0)

        physical_value = prior.value_for(unit=0.2)
        """
        return super().value_for(unit, ignore_prior_limits=ignore_prior_limits)

    @property
    def parameter_string(self) -> str:
        return f"lower_limit = {self.lower_limit}, upper_limit = {self.upper_limit}"