Source code for biogeme.expressions.divide

"""Arithmetic expressions accepted by Biogeme: binary division

Michel Bierlaire
Sat Jun 14 2025, 10:23:07
"""

from __future__ import annotations

import logging

import pandas as pd
from jax import numpy as jnp
from pytensor.tensor import TensorVariable

from biogeme.exceptions import BiogemeError
from biogeme.floating_point import EPSILON
from .base_expressions import ExpressionOrNumeric
from .bayesian import PymcModelBuilderType
from .binary_expressions import BinaryOperator
from .jax_utils import JaxFunctionType
from .numeric_expressions import Numeric

logger = logging.getLogger(__name__)




class Divide(BinaryOperator):
    """
    Division expression
    """

    def __init__(self, left: ExpressionOrNumeric, right: ExpressionOrNumeric):
        """Constructor

        :param left: first arithmetic expression
        :type left: biogeme.expressions.Expression

        :param right: second arithmetic expression
        :type right: biogeme.expressions.Expression
        """
        super().__init__(left, right)
        self.simplified = None
        if isinstance(self.left, Numeric) and self.left.get_value() == 0:
            self.simplified = Numeric(0)
        elif isinstance(self.right, Numeric) and self.right.get_value() == 1:
            self.simplified = self.left



    def deep_flat_copy(self) -> Divide:
        """Provides a copy of the expression. It is deep in the sense that it generates copies of the children.
        It is flat in the sense that any `MultipleExpression` is transformed into the currently selected expression.
        The flat part is irrelevant for this expression.
        """
        left_copy = self.left.deep_flat_copy()
        right_copy = self.right.deep_flat_copy()
        return type(self)(left=left_copy, right=right_copy)


    def __str__(self) -> str:
        return f'({self.left} / {self.right})'

    def __repr__(self) -> str:
        return f'({repr(self.left)} / {repr(self.right)})'



    def get_value(self) -> float:
        """Evaluates the value of the expression

        :return: value of the expression
        :rtype: float
        """
        if self.simplified is not None:
            return self.simplified.get_value()
        left_val = self.left.get_value()
        right_val = self.right.get_value()
        if right_val == 0.0:
            raise BiogemeError("Division by zero in Divide expression.")
        return left_val / right_val




    def recursive_construct_jax_function(
        self, numerically_safe: bool
    ) -> JaxFunctionType:
        """
        Generates a function to be used by biogeme_jax. Must be overloaded by each expression
        :return: the function takes two parameters: the parameters, and one row of the database.
        """
        if self.simplified is not None:
            return self.simplified.recursive_construct_jax_function(
                numerically_safe=numerically_safe
            )
        left_jax: JaxFunctionType = self.left.recursive_construct_jax_function(
            numerically_safe=numerically_safe
        )
        right_jax: JaxFunctionType = self.right.recursive_construct_jax_function(
            numerically_safe=numerically_safe
        )
        if numerically_safe:

            def the_jax_function(
                parameters: jnp.ndarray,
                one_row: jnp.ndarray,
                the_draws: jnp.ndarray,
                the_random_variables: jnp.ndarray,
            ) -> float:
                left_value = left_jax(
                    parameters, one_row, the_draws, the_random_variables
                )
                right_value = right_jax(
                    parameters, one_row, the_draws, the_random_variables
                )
                return left_value * right_value / (right_value**2 + EPSILON)

            return the_jax_function

        def the_jax_function(
            parameters: jnp.ndarray,
            one_row: jnp.ndarray,
            the_draws: jnp.ndarray,
            the_random_variables: jnp.ndarray,
        ) -> float:
            left_value = left_jax(parameters, one_row, the_draws, the_random_variables)
            right_value = right_jax(
                parameters, one_row, the_draws, the_random_variables
            )

            return left_value / right_value

        return the_jax_function




    def recursive_construct_pymc_model_builder(self) -> PymcModelBuilderType:
        """
        Generates recursively a function to be used by PyMc. Must be overloaded by each expression
        :return: the expression in TensorVariable format, suitable for PyMc
        """
        left_pymc = self.left.recursive_construct_pymc_model_builder()
        right_pymc = self.right.recursive_construct_pymc_model_builder()

        def builder(dataframe: pd.DataFrame) -> TensorVariable:
            left_value = left_pymc(dataframe=dataframe)
            right_value = right_pymc(dataframe=dataframe)
            return left_value / right_value

        return builder