Line: 1 to 1 | ||||||||
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## The Transportation Problem in AMPL | ||||||||

Line: 23 to 23 | ||||||||

param Cost {SUPPLY_NODES, DEMAND_NODES}; | ||||||||

Changed: | ||||||||

< < | Now, the mathematical proramme follows directly: | |||||||

> > | Now, the mathematical programme follows directly: | |||||||

Changed: | ||||||||

< < | var Flow {i in SUPPLY_NODES, j in DEMAND_NODES} >= 0, integer; | |||||||

> > | var Flow {SUPPLY_NODES, DEMAND_NODES} >= 0, integer; | |||||||

minimize TotalCost: sum {i in SUPPLY_NODES, j in DEMAND_NODES} Cost[i, j] * Flow[i, j]; | ||||||||

Line: 38 to 38 | ||||||||

Note that we assume the transportation is balanced. | ||||||||

Added: | ||||||||

> > | ## Adding BoundsIn the main discussion of transportation problems, we saw that adding bounds to the flow variables allowed us to easily either bound the transportation of good from a supply node to a demand node or remove an arc from the problem altogether. We can add bounds to our AMPL formulation by declaring 2 new parameters with defaults: param Lower {SUPPLY_NODES, DEMAND_NODES} integer default 0; param Upper {SUPPLY_NODES, DEMAND_NODES} integer default Infinity;and adding them to the `Flow` variable declaration:
var Flow {i in SUPPLY_NODES, j in DEMAND_NODES} >= Lower[i, j], <= Upper[i, j], integer;
## Balancing Transportation Problems | |||||||

-- MichaelOSullivan - 02 Apr 2008 |

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