logistic

class Logistic(OneToOneInversableDerivableTransformer):
    """Transform series by applying logistic function combined with (over) affine function.

    ```math
        \\frac{1}{1+\\exp(-slope \\times (serie-constant))}
    ```

    Args:
        - slope (float): Slope of the affine function.
        - constant (float): y-intercept of the affine function.
    """

    def __init__(self, slope: float, constant: float) -> None:
        self.slope = slope
        self.constant = constant

    @property
    def parameters(self) -> Dict[str, float]:
        return self.__dict__

    # ------- METHODS -------

    def transform(self, serie: np.ndarray, copy=False) -> np.ndarray:
        serie = super().transform(serie, copy)

        return self._transformer(serie, self.slope, self.constant)

    def inverse_transform(self, serie: np.ndarray, copy=False) -> np.ndarray:
        serie = super().inverse_transform(serie, copy)

        return self._inverse_transformer(serie, self.slope, self.constant)

    def derivative_transform(self, serie: np.ndarray, copy=False) -> np.ndarray:
        serie = super().derivative_transform(serie, copy)

        return self._derivative_transformer(serie, self.slope, self.constant)

    # ------- TRANSFORMERS -------

    @staticmethod
    def _transformer(serie: np.ndarray, slope, constant) -> np.ndarray:
        with np.errstate(over="raise", divide="raise"):
            return 1 / (1 + np.exp(-slope * (serie - constant)))

    @staticmethod
    def _inverse_transformer(serie: np.ndarray, slope, constant) -> np.ndarray:
        with np.errstate(over="raise", divide="raise"):
            return constant - np.log(1 / serie - 1) / slope

    @staticmethod
    def _derivative_transformer(serie: np.ndarray, slope, constant) -> np.ndarray:
        with np.errstate(over="raise", divide="raise"):
            return slope * np.exp(-slope * (serie - constant)) / ((1 + np.exp(-slope * (serie - constant))) ** 2)

    # ------- CHECKERS -------

    def check_params(self, serie: np.ndarray):
        """Check if parameters respect their application scope."""
        pass