.. py:method:: log_prob(value, mean=None, sd=None)

    Evaluate log probability of the value of the HalfNormal distribution.

    Parameters
        - **value** (Tensor) - the value to compute.
        - **mean** (Tensor, optional) - the mean of the distribution. Default: ``None`` .
        - **sd** (Tensor, optional) - the standard deviation of the distribution. Default: ``None`` .

    Returns
        Tensor, the log value of the probability.
