[Fix][Readability] Improving the Capsule Network example. (#5985)

Co-authored-by: Hongzhi (Steve), Chen <chenhongzhi.nkcs@gmail.com>

examples/pytorch/capsule/DGLRoutingLayer.py

@@ -68,15 +68,16 @@ def squash(s, dim=1):
 
 
 def init_graph(in_nodes, out_nodes, f_size, device="cpu"):
-    g = dgl.DGLGraph()
-    g.set_n_initializer(dgl.frame.zero_initializer)
-    all_nodes = in_nodes + out_nodes
-    g.add_nodes(all_nodes)
+    src, dst = [], []
     in_indx = list(range(in_nodes))
     out_indx = list(range(in_nodes, in_nodes + out_nodes))
     # add edges use edge broadcasting
     for u in in_indx:
-        g.add_edges(u, out_indx)
+        src += [u] * len(out_indx)
+        dst += out_indx
+
+    g = dgl.graph((src, dst))  # dgl.graph once;
+    g.set_n_initializer(dgl.frame.zero_initializer)
     g = g.to(device)
     g.edata["b"] = th.zeros(in_nodes * out_nodes, 1).to(device)
     return g