Choco model for Transshipment problem

[Andreea Ungurean]

Hi,

I have the following transshipment problem:

Number of sources: 2     ( found in code as supplyLength)

Number of destinations: 3   (found in code as demandLength)

The demand for each of the 3 destination points: 

[150, 100, 150]    (found in code as demand[])

The quantity available at each 2 source points: 

[300, 100]       (found in code as supply[])

The number of transshipment points 2    (found in code as transPoints)

The matrix of costs from a source to a transshipment point :   (found in code as costsWT[][])

7 5 

3 4 

The matrix of costs from a transshipment point to a destination point :  (found in code as costsTC[][])

8 5 7 

5 6 10 

I am stuck at writing the constraint for the transshipment points - the sum of all flows that enter a transshipment point = the sum of all flows that leaves the transshipment point. ( in my case 

7 + 3 = 8 + 5 + 7

5 + 4 = 5 + 6 + 10

)

Below is what I have so far:

IntVar[][] result = new IntVar[supplyLength + transPoints][demandLength + transPoints];

for (int i = 0; i < supplyLength + transPoints ; i++) {

for (int j = 0; j < demandLength + transPoints; j++) {

result[i][j] = model.intVar("result_" + i + j, 0,100);

}

}

//sum of source row values <= supply

for (int i = 0; i < supplyLength; i++) {

   model.sum(result[i],"<=",supply[i]).post();   

}

//sum of column values = demand

int demandIndex = 0;

for(int i = transPoints; i < demandLength + transPoints; i++) {

         IntVar[] col = new IntVar[supplyLength + transPoints];

      for(int j = 0; j < supplyLength + transPoints; j++) {

             col[j] = result[j][i];

       }

    model.sum(col, "=", demand[demandIndex]).post(); 

    demandIndex ++;

   }

IntVar tot_cost = model.intVar("tot_cost", 0, 9999, true);

//flow in = flow out ??

model.setObjective(Model.MINIMIZE, tot_cost);

Solver solver = model.getSolver();

while(solver.solve())

{

System.out.println(solver.getSolutionCount() + "----------" );

}

Can you please help me understand how to write these constraints and tell me if it's ok to use a result matrix?

Thank you!

Ungurean Andreea

[cpru...@gmail.com]

Hi

Did you find out how to achieve this finally ?

CP