def _call(self, x):
        """Return ``self(x)``."""
        if isinstance(self.domain, ProductSpace):
            norm = PointwiseNorm(self.domain, 2)(x)
        else:
            norm = x.ufuncs.absolute()

        if self.gamma > 0:
            tmp = norm.ufuncs.square()
            tmp *= 1 / (2 * self.gamma)

            index = norm.ufuncs.greater_equal(self.gamma)
            tmp[index] = norm[index] - self.gamma / 2
        else:
            tmp = norm

        return tmp.inner(tmp.space.one())