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MAXIMAL FLOW PROBLEM   357


                                      Figure 8.15 The Management Scientist Solution for the Regional Computer Centre
                                      Minimal Spanning Tree Problem
                                                           ****  NETWORK DESCRIPTION  ****

                                                                 6 NODES AND 11 ARCS

                                                     ARC    START NODE    END NODE    DISTANCE
                                                     ---    ----------    --------    --------
                                                      1         1            2           20
                                                      2         1            3           40
                                                      3         1            4           30
                                                      4         1            5           50
                                                      5         1            6           40
                                                      6         2            5           40
                                                      7         3            4           10
                                                      8         3            5           30
                                                      9         3            6           30
                                                     10         4            6           20
                                                     11         5            6           40

                                                                MINIMAL SPANNING TREE
                                                                *********************

                                                     START NODE       END NODE       DISTANCE
                                                     ----------       --------       --------
                                                           1              2              20
                                                           1              4              30
                                                           4              3              10
                                                           4              6              20
                                                           3              5              30

                                                             TOTAL LENGTH               110








                                8.3     Maximal Flow Problem


                                      The objective in a maximal flow problem is to determine the maximum amount of
                                      flow (vehicles, messages, fluid, etc.) that can enter and exit a network system in a
                                      given period of time. In this problem, we attempt to transmit flow through all arcs of
                                      the network as efficiently as possible. The amount of flow is limited due to capacity
                                      restrictions on the various arcs of the network. For example, highway types limit
                                      vehicle flow in a transportation system, while pipe sizes limit oil flow in an oil
                                      distribution system. The maximum or upper limit on the flow in an arc is referred
                                      to as the flow capacity of the arc. Even though we do not specify capacities for the
                      L. R. Ford and D. R.  nodes, we do assume that the flow out of a node is equal to the flow into the node.
                      Fulkerson set out the  As an example of the maximal flow problem, consider the road network system
                      procedure for solving the
                      maximal flow problem in  passing through Glasgow, Scotland. The vehicle flow travelling west to east reaches a
                      1955.           level of 15 000 vehicles per hour at peak times. Due to a summer highway





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