Difference: TransportationProblemInAMPL (2 vs. 3)

Revision 32008-04-02 - MichaelOSullivan

Line: 1 to 1

META TOPICPARENT	name="AMPLGuide"

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 Bounds

In 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

View topic | History: r9 < r8 < r7 < r6 | More topic actions...