fixed up symmetric kern

GPy/kern/constructors.py

@@ -464,7 +464,7 @@ def symmetric(k):
     This constructor builds a covariance function of this form from the initial kernel
     """
     k_ = k.copy()
-    k_.parts = [symmetric.Symmetric(p) for p in k.parts]
+    k_.parts = [parts.symmetric.Symmetric(p) for p in k.parts]
     return k_
 
 def coregionalize(output_dim,rank=1, W=None, kappa=None):

GPy/kern/parts/symmetric.py

@@ -56,7 +56,7 @@ class Symmetric(Kernpart):
         AX = np.dot(X,self.transform)
         if X2 is None:
             X2 = X
-            ZX2 = AX
+            AX2 = AX
         else:
             AX2 = np.dot(X2, self.transform)
         self.k.dK_dtheta(dL_dK,X,X2,target)