def inv_symlog(x: torch.Tensor) -> torch.Tensor:
    """
    **Overview**:
        The inverse form of symlog. Given the input tensor ``x`` , this function will return the unnormalized tensor.
    """
    # The formula of the unnormalization is: $$symexp(x) = sign(x)(\exp{|x|}-1)$$
    return torch.sign(x) * (torch.exp(torch.abs(x)) - 1)

    **Overview**:
        The inverse form of symlog. Given the input tensor ``x`` , this function will return the unnormalized tensor.
    
chapter4_reward/value_rescale.py