def _call(self, x):
        """Return the KL-diveregnce in the point ``x``.

        If any components of ``x`` is non-positive, the value is positive
        infinity.
        """
        # Lazy import to improve `import odl` time
        import scipy.special

        with np.errstate(invalid='ignore', divide='ignore'):
            if self.prior is None:
                res = (x - 1 - np.log(x)).inner(self.domain.one())
            else:
                xlogy = scipy.special.xlogy(self.prior, self.prior / x)
                res = (x - self.prior + xlogy).inner(self.domain.one())

        if not np.isfinite(res):
            # In this case, some element was less than or equal to zero
            return np.inf
        else:
            return res
Return the KL-diveregnce in the point ``x``.

        If any components of ``x`` is non-positive, the value is positive
        infinity.