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Q2 Z2,(Q2) Z2(Q2) - Institute for Water Resources - U.S. Army

Q2 Z2,(Q2) Z2(Q2) - Institute for Water Resources - U.S. Army

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At about this same time S. Enke was also grappling with the trans-<br />

portation problem. His model as it evolved was also <strong>for</strong> a world com-<br />

posed of many markets and one commodity. However, he hypothesized that<br />

if each region was conceived to have linear product supply and demand<br />

functions, and unit transport charges between regions were independent<br />

of volume, the (transport cost minimizing and market clearing) flows<br />

could be determined by analogy with the electrical network studies of<br />

Clerk Maxwell and Kirchhoff. 5 While his multi-market model was a maze<br />

of resistors, power sources and current flows, he was able to present<br />

a verbal discussion of the economic solution <strong>for</strong> the three-market case<br />

based upon excess supply and demand functions. 6 Thus, while Koopmans<br />

and Hitchcock were able to develop the fixed quantities case to a point<br />

where a solution was possible, Enke's contribution was to suggest an<br />

transport costs. These are actually allocation problems which ignore<br />

production and consumption conditions both in the product market and,<br />

essentially, in the transportation market.<br />

In the multi-mode models it is possible <strong>for</strong> a modal split to occur.<br />

However, it must be of the "all or nothing" variety, that is either<br />

all of the traffic between two markets will be carried by one mode, or<br />

one mode will carry all it can handle be<strong>for</strong>e another will be brought<br />

into operation.<br />

See, <strong>for</strong> example: K. B. Haley, "The Multi-Index Problem,"<br />

Operations Research, Vol. 11 No. 3 (May, June), 1963, 368-379, and<br />

. R. W. Lewis, E. F. Rosholdt, and W. L. Wilkinson, "A Multi-Mode Transportation<br />

Network Model," Naval Research Logistics Quarterly, Vol. 12,<br />

Nos. 3 & 4 (Sept., Dec.), 1965, 261-274.<br />

5. S. Enke, "Equilibrium Among Spatially Separated Markets: Solution<br />

by Electric Analogue," Econometrica, Vol. 19 (Jan. 1951), 40-47.<br />

6. For an excellent discussion of this three-market case in geometric<br />

<strong>for</strong>m.see: Eugene Silberberg, The Demand <strong>for</strong> Inland <strong>Water</strong>way<br />

Transportation, unpublished Ph.D. dissertation, Purdue University,<br />

1964.<br />

9

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