Minor change to updating of gradients in multioutput kernel

GPy/kern/src/kern.py

@@ -201,6 +201,12 @@ class Kern(Parameterized):
     def reset_gradients(self):
         raise NotImplementedError
     
+    def get_gradient(self):
+        return self.gradient.copy()
+    
+    def append_gradient(self,gradient):
+        self.gradient += gradient
+
     def update_gradients_expectations(self, dL_dpsi0, dL_dpsi1, dL_dpsi2, Z, variational_posterior):
         """
         Set the gradients of all parameters when doing inference with

GPy/kern/src/multioutput_kern.py

@@ -94,14 +94,14 @@ class MultioutputKern(CombinationKernel):
         return target
     
     def _update_gradients_full_wrapper(self, cov_struct, dL_dK, X, X2):
-        gradient = cov_struct['kern'].gradient.copy()
+        gradient = cov_struct['kern'].get_gradient()
         cov_struct['update_gradients_full'](dL_dK, X, X2)
-        cov_struct['kern'].gradient += gradient
+        cov_struct['kern'].append_gradient(gradient)
     
     def _update_gradients_diag_wrapper(self, kern, dL_dKdiag, X):
-        gradient = kern.gradient.copy()
+        gradient = kern.get_gradient()
         kern.update_gradients_diag(dL_dKdiag, X)
-        kern.gradient += gradient
+        kern.append_gradient(gradient)
         
     def reset_gradients(self):
         for kern in self.kern: kern.reset_gradients()