Update example with spmatrix. (#5219)

* update

* graph

Co-authored-by: Steve <ubuntu@ip-172-31-34-29.ap-northeast-1.compute.internal>

examples/sparse/sign.py

@@ -102,9 +102,9 @@ if __name__ == "__main__":
 
     # Create the sparse adjacency matrix A (note that W was used as the notation
     # for adjacency matrix in the original paper).
-    src, dst = g.edges()
+    indices = torch.stack(g.edges())
     N = g.num_nodes()
-    A = dglsp.from_coo(dst, src, shape=(N, N))
+    A = dglsp.spmatrix(indices, shape=(N, N))
 
     # Calculate the symmetrically normalized adjacency matrix.
     I = dglsp.identity(A.shape, device=dev)