nngraph: width = radius / 2

pygsp/graphs/nngraphs/nngraph.py

@@ -217,7 +217,8 @@ class NNGraph(Graph):
         Control the width, also known as the bandwidth, :math:`\sigma` of the
         kernel by scaling the distances as ``distances / kernel_width`` before
         calling the kernel function.
-        By default, it is set to the average of all computed distances.
+        By default, it is set to the average of all computed distances for
+        ``kind='knn'`` and to half the radius for ``kind='radius'``.
         When building a radius graph, it's common to set it as a function of
         the radius, such as ``radius / 2``.
     backend : string, optional
@@ -362,7 +363,10 @@ def __init__(self, features, standardize=False,
         W = utils.symmetrize(W, method='fill')
 
         if kernel_width is None:
-            kernel_width = np.mean(W.data) if W.nnz > 0 else np.nan
+            if kind == 'knn':
+                kernel_width = np.mean(W.data) if W.nnz > 0 else np.nan
+            elif kind == 'radius':
+                kernel_width = radius / 2
 
         if not callable(kernel):
             try:

pygsp/tests/test_graphs.py

@@ -374,7 +374,7 @@ def test_nngraph(self, n_vertices=24):
                     else:
                         params['backend'] = backend
                         if backend == 'flann':
-                            graph = Graph(random_seed=0, **params)
+                            graph = Graph(random_seed=40, **params)
                         else:
                             graph = Graph(**params)
                         np.testing.assert_allclose(graph.W.toarray(),