def __init__(self, prior_lambda=None, prior_strength=1.0):
        """
        Exponential distribution.

        https://en.wikipedia.org/wiki/Exponential_distribution

        - Univariate continuous distribution.
        - Support: :math:`\\mathbb{R}_{>0}`.
        - Parameter: rate :math:`\\lambda > 0`.

        Parameters
        ----------
        prior_lambda
            rate :math:`\\lambda` of the prior exponential distribution (default: None).
        prior_strength
            strength of the loss regularisation induced by the prior
        """
        self.prior_lambda = prior_lambda
        _check_strict_positive(self.prior_lambda, "lambda")
        self.softplus = nn.Softplus()
        super().__init__(
            likelihood_type=LikelihoodType.Exponential,
            parameter_names=["lambda"],
            prior_strength=prior_strength,
        )

        Exponential distribution.

        https://en.wikipedia.org/wiki/Exponential_distribution

        - Univariate continuous distribution.
        - Support: :math:`\mathbb{R}_{>0}`.
        - Parameter: rate :math:`\lambda > 0`.

        Parameters
        ----------
        prior_lambda
            rate :math:`\lambda` of the prior exponential distribution (default: None).
        prior_strength
            strength of the loss regularisation induced by the prior
        
darts/utils/likelihood_models/torch.py