def METHOD_NAME(self, x):
    """ See :meth:`LogPDF.evaluateS1()`.
    """
    L = self.__call__(x)
    r = self._r0
    norm = np.linalg.norm(x)
    sigma = self._sigma
    cons = -(norm - r) / (norm * sigma**2)
    dL = np.array([var * cons for var in x])
    return L, dL