def dKd_dVar(self, X, X2=None):
		"""
		Derivative of Kernel function wrt variance applied on inputs X and X2.
		In the stationary case there is an inner function depending on the
		distances from X to X2, called r.

		dKd_dVar(X, X2) = dKdVar_of_r((X-X2)**2)
		"""
		r = self._scaled_dist(X, X2)
		return self.dKdVar_of_r(r)