Use output_graph to generate a topology graph with nodes

[sunsirui]

Hello:
In the user manual <manual.md> chapter ”Section 4.3: Fat Tree“,
How “Figure25” was generated, I used the following steps:

1. Configure in the parameters.ini file:
   topology {
   name = fat_tree
   num_core_switches = 4
   num_agg_subtrees = 2
   agg_switches_per_subtree = 4
   leaf_switches_per_subtree = 4
   down_ports_per_core_switch = 8
   up_ports_per_agg_switch = 4
   down_ports_per_agg_switch = 4
   up_ports_per_leaf_switch = 4
   concentration = 4
   output_graph = fattree4.dot
   }
   As a result the fattree4.dot file is generated.
2. Use the command: dot -Tpdf fattree4.dot -o fattree4.pdf
   A switch topology diagram similar to ”Figure25“ will be generated (the nodes under the switch are not displayed)

Can you tell me how the whole graph of switch connected nodes in Figure 25 is generated?

Thanks a lot.