Improved code-reuse between Add and Prod kernels

GPflow/kernels.py

@@ -244,21 +244,21 @@ def make_kernel_names(kern_list):
 
 
 
-class Add(Kern):
+class Combination(Kern):
     """
-    Add  a list of kernels together.
+    Combine  a list of kernels, e.g. by adding or multiplying (see inherriting classes).
 
-    The names of the kernels are generated from their class names.
+    The names of the kernels to be combined are generated from their class names.
     """
     def __init__(self, kern_list):
         for k in kern_list:
             assert isinstance(k, Kern), "can only add Kern instances"
         Kern.__init__(self, input_dim=np.max([k.input_dim for k in kern_list]))
 
-        #add kernels to a list, flattening out instances of Add kerns therein.
+        #add kernels to a list, flattening out instances of this class therein.
         self.kern_list = []
         for k in kern_list:
-            if isinstance(k, Add):
+            if isinstance(k, self.__class__):
                 self.kern_list.extend(k.kern_list)
             else:
                 self.kern_list.append(k)
@@ -267,36 +267,15 @@ def __init__(self, kern_list):
         names = make_kernel_names(self.kern_list)
         [setattr(self, name, k) for name, k in zip(names, self.kern_list)]
 
+class Add(Combination):
     def K(self, X, X2=None):
         return reduce(tf.add, [k.K(X, X2) for k in self.kern_list])
 
     def Kdiag(self, X):
         return reduce(tf.add, [k.Kdiag(X) for k in self.kern_list])
 
 
-class Prod(Kern):
-    """
-    Multiply  a list of kernels together.
-
-    The names of the kernels are generated from their class names.
-    """
-    def __init__(self, kern_list):
-        for k in kern_list:
-            assert isinstance(k, Kern), "can only Prod Kern instances"
-        Kern.__init__(self, input_dim=np.max([k.input_dim for k in kern_list]))
-
-        #add kernels to a list, flattening out instances of Prod kerns therein.
-        self.kern_list = []
-        for k in kern_list:
-            if isinstance(k, Prod):
-                self.kern_list.extend(k.kern_list)
-            else:
-                self.kern_list.append(k)
-
-        #generate a set of suitable names and add the kernels as atributes of this one.
-        names = make_kernel_names(self.kern_list)
-        [setattr(self, name, k) for name, k in zip(names, self.kern_list)]
-
+class Prod(Combination):
     def K(self, X, X2=None):
         return reduce(tf.mul, [k.K(X, X2) for k in self.kern_list])