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<br />. <br /> <br />o <br /> <br />000537 <br /> <br />5. MODSIM utilizes physically-based methods for including <br />stream-aquifer interaction in a river basin due to depletion <br />effects of pumping and subsurface return flows to the river. <br />This feature allows MODSIM to be used for development of <br />comprehensive strategies for conjunctive use of surface and <br />groundwater in a water supply system. <br /> <br />6. MODSIM is in the process of being integrated into a <br />comprehensive decision support system called the Graphical <br />Display System (GDS) for application on advanced UNIX <br />workstation operating under the X-Window/MOTIF <br />environment. The GDS is useful for providing a graphical-based <br />shell for water supply system analysis using MODSIM. The user <br />is allowed to digitize and display map information for the river <br />basin network and interactively input all necessary data. <br />MODS 1M is then automatically accessed for performing the <br />river basin network calculations. Convenient, user-selective <br />output of information for any part of the system is provided, all <br />in a powerful, color-graphic computing environment. <br /> <br />NETWORK OPTIMIZER IN MODSIM <br /> <br />The network optimizer employed in MODSIM is actually a <br />special case of linear programming. Fulkerson (1961) <br />discovered that linear programming problems of special <br />structure represented by flows through links or arcs could be <br />solved by an efficient procedure called the "out-of-kilter" <br />algorithm. In comparing problems solved by the simplex <br />method of linear programming and modem network <br />algorithms such as Lagrangian Relaxation, researchers have <br />shown minimum cost network flow problems to be roughly <br />150 to 200 times faster than state-of-the-art linear <br />programming codes, and require considerably less computer <br />memory. <br /> <br />5 <br />