3.4.1 Combinatorial aspects of network structure
Many problems in network theory are well known because they are easy to state, can be solved by trivial methods for small blackboard examples, but which are virtually intractable in large scale, realistic situations. Most of the difficulties arise from the explosive, combinatorial nature of the mathematics. Consider, for example, the building of a network to link the three towns shown in Figure 3.11. Given the cost of constructing each link, we can easily specify the total costs of the eight alternatives open to us. These range from 75 cost units for building a complete network, down to zero for inaction, and a choice can be made depending on the budget and objectives available.