add dw property

graphtools/base.py

@@ -658,6 +658,24 @@ def P(self):
             self._diff_op = normalize(self.kernel, "l1", axis=1)
             return self._diff_op
 
+    @property
+    def dw(self):
+        """Weighted degree vector (cached)
+
+        Return or calculate the degree vector
+
+        Returns
+        -------
+
+        dw : array-like, shape=[n_samples]
+            Row sums of graph kernel
+        """
+        try:
+            return self._dw
+        except AttributeError:
+            self._dw = utils.to_array(self.kernel.sum(axis=1))
+            return self._dw
+
     @property
     def diff_aff(self):
         """Symmetric diffusion affinity matrix
@@ -675,7 +693,7 @@ def diff_aff(self):
             symmetric diffusion affinity matrix defined as a
             doubly-stochastic form of the kernel matrix
         """
-        row_degrees = utils.to_array(self.kernel.sum(axis=1))
+        row_degrees = self.dw
         if sparse.issparse(self.kernel):
             # diagonal matrix
             degrees = sparse.csr_matrix(
@@ -940,6 +958,20 @@ def K():
         """
         raise NotImplementedError
 
+    @property
+    def dw(self):
+        """Weighted degree vector (cached)
+
+        Return or calculate the degree vector
+
+        Returns
+        -------
+
+        dw : array-like, shape=[n_samples]
+            Row sums of graph kernel
+        """
+        return pygsp.graphs.Graph.dw(self)
+
     def _build_weight_from_kernel(self, kernel):
         """Private method to build an adjacency matrix from
         a kernel matrix