The figure below shows a network of one-way streets. An ambulance
station is located at intersection A. The monthly demands for
ambulance service at the intersections are shown in the square
brackets adjacent to the nodes. There are two costs associated
with each street as shown in the parentheses adjacent to the arcs.
The first number is the cost of installing special communications
equipment that control the street lights. This is a fixed cost
per month that is expended if the street is selected for a route.
It is independent of the number of times the street is used. The
second number on an arc is the unit cost of a trip down the street.
We want a mathematical programming formulation
whose solution will determine the minimum cost selection of
streets that will serve all the intersections shown. Use a network
model with additional variables defined to represent the fixed