Fix negative_sample_adj_mat().

src/triacontagon/sampling.py

@@ -135,7 +135,10 @@ def negative_sample_adj_mat(adj_mat: torch.Tensor) -> torch.Tensor:
 
     print('neg_neighbors:', neg_neighbors)
 
-    edges_neg = torch.cat([ edges_pos[:, 0].view(-1, 1),
+    pos_vertices = torch.repeat_interleave(torch.arange(len(adj_mat)),
+        row_count)
+
+    edges_neg = torch.cat([ pos_vertices.view(-1, 1),
         neg_neighbors.view(-1, 1) ], 1)
 
     adj_mat_neg = torch.sparse_coo_tensor(indices = edges_neg.transpose(0, 1),