[GraphBolt] update notebooks about numpy edges (#6936)

docs/source/stochastic_training/ondisk-dataset-specification.rst

@@ -122,8 +122,10 @@ The ``graph`` field is used to specify the graph structure. It has two fields:
       homogeneous graphs. For heterogeneous graphs, it is the edge type.
     - ``format``: ``string``
 
-      The ``format`` field is used to specify the format of the edge data. It can
-      only be ``csv`` for now.
+      The ``format`` field is used to specify the format of the edge data. It
+      can be ``csv`` or ``numpy``. If it is ``csv``, no ``index`` and ``header``
+      fields are needed. If it is ``numpy``, the array requires to be in shape
+      of ``(2, num_edges)``. ``numpy`` format is recommended for large graphs.
     - ``path``: ``string``
 
       The ``path`` field is used to specify the path of the edge data. It is

notebooks/stochastic_training/ondisk_dataset_heterograph.ipynb

@@ -103,10 +103,11 @@
       "cell_type": "markdown",
       "source": [
         "### Generate graph structure data\n",
-        "For heterogeneous graph, we need to save different edge edges(namely node pairs) into separate **CSV** files.\n",
+        "For heterogeneous graph, we need to save different edge edges(namely node pairs) into separate **Numpy** or **CSV** files.\n",
         "\n",
-        "**Note**:\n",
-        "when saving to file, do not save index and header.\n"
+        "Note:\n",
+        "- when saving to **Numpy**, the array requires to be in shape of `(2, N)`. This format is recommended as constructing graph from it is much faster than **CSV** file.\n",
+        "- when saving to **CSV** file, do not save index and header.\n"
       ],
       "metadata": {
         "id": "qhNtIn_xhlnl"

notebooks/stochastic_training/ondisk_dataset_homograph.ipynb

@@ -103,10 +103,11 @@
       "cell_type": "markdown",
       "source": [
         "### Generate graph structure data\n",
-        "For homogeneous graph, we just need to save edges(namely node pairs) into **CSV** file.\n",
+        "For homogeneous graph, we just need to save edges(namely node pairs) into  **Numpy** or **CSV** file.\n",
         "\n",
         "Note:\n",
-        "when saving to file, do not save index and header.\n"
+        "- when saving to **Numpy**, the array requires to be in shape of `(2, N)`. This format is recommended as constructing graph from it is much faster than **CSV** file.\n",
+        "- when saving to **CSV** file, do not save index and header.\n"
       ],
       "metadata": {
         "id": "qhNtIn_xhlnl"