def _param_grad_helper(self, dL_dK, X, X2, target):
if (X2 is None) or (X2 is X):<EOL><INDENT>dL_dKdiag = dL_dK.flat[::dL_dK.shape[<NUM_LIT:0>]+<NUM_LIT:1>]<EOL>self.dKdiag_dtheta(dL_dKdiag, X, target)<EOL><DEDENT>
Derivative of the covariance with respect to the parameters.