def nl(x, gamma):
    """
    Nonlinearity of the form

    .. math::

        f_{\\gamma}(x) = \\frac{1}{1-\\gamma x}

    Args:
        x (:class:`numpy.array`): signal
        gamma (float): Nonlinearity parameter

    Note:
        The integral of ``gamma * nl(x, gamma)`` is

        .. math::

            \\int \\frac{\\gamma}{1 - \\gamma x} = -\\log (1 - \\gamma x)

    """
    return 1.0/(1.0-gamma*x)