Revised ResourcePrice class and methods. Added tests for problem...

Revised ResourcePrice class and methods. Added tests for problem simplification routines. Started problem identification method.

src/topupopt/data/dhn/utils.py

@@ -153,7 +153,7 @@ def plot_network_layout(network: Network,
         (max_linewidth-min_linewidth)*
         iteration/(len(list_sorted_dn)-1)
         for iteration, _ in enumerate(list_sorted_dn)
-        ] if len(list_sorted_dn) == 1 else [(max_linewidth+min_linewidth)/2]
+        ] if len(list_sorted_dn) != 1 else [(max_linewidth+min_linewidth)/2]
         
     # *************************************************************************
     # *************************************************************************